Amnesia

Amnesia refers to a loss of memory, usually involving forgetting details of the past.

Amnesia is a commonly used plot device on Smallville, used to advance the plot in a few main ways:

• To reveal a secret, and then have one person forget. The most common example is the biggest secret of all: Clark Kent's secret. Other examples include Lionel Luthor confessing to killing his parents, a secret which Lex Luthor forgot after undergoing electroshock therapy; also, Clark Kent asked Jor-El not to restore Chloe Sullivan's memories of his secret, after almost all of her memories were deleted by Brainiac. (Abyss)

• To reveal feelings, and then have the other person forget. Examples include Chloe kissing Clark in Hug, and then forgetting after the kryptonite handshake wore off, and Lois kissing Clark in Crimson and then forgetting after the red kryptonite wore off.

• Total Amnesia. As a plot device, total amnesia allows a character to rediscover who they are and what motivates them. It also allows supporting characters to better understand what it's like to be that person. Finally, it allows former enemies to interact and even become close. Examples include Clark Kent forgetting who he was in Blank, during which Chloe Sullivan helped him adjust; Kara Kent forgetting her identity in Blue, during which she became close to Lex Luthor; and Chloe Sullivan suffering almost total amnesia due to Brainiac's infection, during which time she became close to Davis Bloome (Abyss).

Amnesia has many possible causes:

Possession

Possession is when one being takes control of a body which is not its own. Each possession is usually done by an entity lacking a physical body: a Phantom Zone wraith, a Kryptonian spirit, a dead human, or a dead witch. The sole exception is body transfers using Kryptonian technology, in which two bodies exchange spirits.

• In Season 4's Crusade, Lana received the Mark of Transference from the Countess Margaret Isobel Thoreaux, allowing Isobel's spirit to possess her. Lana woke up in her room later with no memory of what had happened after she received the tattoo.
• In Season 4's Transference, Lionel discovered Clark's powers when they switched bodies using the Crystal of Water. When their bodies were switched back, Lionel had no recollection of the past few days.
• In Season 4's Spell, Lana, Lois, and Chloe were all possessed by witches who then witnessed his powers. After Clark destroyed Countess Isobel's spell book with heat vision, the three women were knocked unconscious and when they awoke, they had forgotten Clark's secret.
• In Season 4's Spirit, Lana is possessed by Dawn Stiles and witnesses Clark superspeed into the locker room and save Billy Durden from electrocution. Shortly later, Dawn's spirit jumps into another student and Lana forgets everything she witnessed during her possession.
• In Season 4's Commencement, when Lionel was shocked into catatonia by the Kryptonian Crystal of Water, he spent weeks in a trance. He didn't remember any of the trance after he recovers.
• In Season 5, Lionel did not remember any of his actions from when he functioned as Jor-El's oracle. (Hidden, Oracle)
• In Season 6's Zod, General Zod possessed Lex Luthor and learned all about Clark's powers... but when Zod was banished using the Crystal of El, Lex had no memory of Zod or Clark's powers.
• In Season 6's Fallout, a Zoner named Baern possessed a human named Lamar, and does battle with Clark at the Kent Farm and the Fortress of Solitude. Clark later used the Crystal of El to send Baern back to the Phantom Zone, and Lamar recovered - with no memory of Clark's powers, or the last six weeks of his life.
• In Season 6's Phantom, a young boy named Philipe Lamont was possessed by the phantom Bizarro. While in Philipe's body, Bizarro killed a human and searched for a Kryptonian host. After Bizarro left his body, Philipe forgot that Clark is a Kryptonian.
• In Season 8's Bloodline, Faora, wife of General Zod, possesses Lois in order to locate Doomsday. Once she is sent back to the phantom zone Lois has no memory of the possession.

Biological

• In Season 1's Nicodemus, Pete witnessed Clark's super speed while under the influence of the Nicodemus flower. After he recovered from the infection, he had no memory of Clark's powers. Lana and Jonathan also had no memory of their actions under the influence of the flower after they were cured.
• In Season 2's Rush, Clark demonstrates his powers for Chloe while she is under the influence of the Kawatche Caves parasites. When she recovers, she has no memory of what happened while she was infected. Pete also did not remember what happened when he was infected.
• In Season 5's Thirst, Lana realized Clark has powers when she sucked his blood as a vampire and acquired his heat vision. After being cured, Lana only remembered the "warmth and love and overwhelming feeling of strength" she felt after biting him.
• In Season 6's Freak, Chloe is abducted by Dr. Robert Bethany and implanted with a tracking device. Afterwards she has no memory of what happened, suggesting that Level 33.1 has mastered the ability to erase memories.
• In Season 7's Cure, Sasha Woodman lost the memories from six years of her life after undergoing surgery by Dr. Curtis Knox's procedure to "cure" her meteor freak powers.
• In Season 10's Finale, Part 2, Tess attacked Lex with a neurotoxin from Summerholt Institute that penetrates dermal tissue to paralyze all cognitive recognition. As a result, he lost all his memories within 30 seconds.

Time travel

• In Season 5's Reckoning, Clark revealed his powers to Lana (and Lex)... and then reset time using Jor-El's time crystal, so they promptly forgot what happened.
• In Season 8's Infamous, Clark revealed his secret to Lois and the entire world, so he wouldn't be blackmailed by Linda Lake. But it backfired and the world turned against him, so he used the Legion ring to go back and stop Linda and everyone (including Lois) forgot his secret.
• In Season 9's Savior, Lois returns from the future, conveniently forgetting everything that had transpired there.

Kryptonite

• In Season 4's Onyx, Lex was split into two personalities by black kryptonite: good and evil Lex. The evil Lex learned about Clark's powers and his vulnerability to kryptonite. After the two personalities were recombined using black kryptonite, Lex conveniently only remembered the experiences of the good Lex, thus he had no memory of Clark's secret.
• In Season 6's Crimson, Clark jumped from the Daily Planet to Queen Tower with Lois in her arms... while they were both under the influence of red kryptonite. When the red kryptonite wore off, she forgot everything that had happened while she was under the influence.

Interestingly, Clark never forgets anything that happens to him while he becomes Kal while under the influence of red kryptonite, even after it wears off, presumably due to his Kryptonian nature.

Electricity

• In Season 1's Pilot, Jeremy Creek witnessed Clark's super speed and invulnerability. Jeremy later accidentally used his own powers to electrocute himself; when he came to, he had near total amnesia.
• In Season 3's Shattered, Lex saw a car hit Clark. In the next episode (Asylum), Lex was given electroshock therapy which caused him to completely forget about Clark's secret.

Metahumans

• In Season 1's Hug, Kyle Tippet used his kryptonite handshake to convince Chloe to kiss Clark. Afterwards, she had no memory of what just happened. Later, Lex Luthor witnessed Clark's superpowers while under the influence of Bob Rickman's kryptonite handshake, but after he was knocked out by Clark he forgot what he had just seen.
• In Season 3's Delete, Molly Griggs brainwashed Clark, Lana, Jonathan, and Martha through e-mail messages. After the hypnotism wore off, the hypnotized victims had no memory of what had just happened.
• In Season 4's Blank, Sheriff Adams, Lois, and Chloe see Clark catch two large electrical columns before they crush Chloe. Kevin Grady uses his memory erasure powers to erase the last few minutes of memory from their minds. Interestingly, when Kevin uses those same powers on Clark earlier, he had lost an entire lifetime of his memories... until he interferes with a Summerholt experiment which inadvertently restored all of his memories - except for the 24 hours since he had gotten amnesia. This shows that Clark's memory system may work differently from humans'.
• In Season 6's Progeny, Chloe Sullivan is mind-controlled several times by her mother, Moira Sullivan. Afterward, she has no recollection of assaulting Lex Luthor, harassing the security guards where her mother was being treated, attacking Clark, or shooting a grenade launcher at Lex at Belle Reve.
• In Season 8's Identity, Sebastian Kane demonstrated the ability to read peoples' minds and selectively remove memories.

Kryptonian

• In Season 4's Crusade, Clark returned to Smallville as Kal-El. He claimed to not remember who he was and did not recognize his mother.
• In Season 7's Lara, Zor-El used a Crystal of El to erase his daughter Kara's memories of a visit to Earth, including his attempts to seduce his brother's wife, Lara-El.
• In Season 7's Blue, Kara's memory (and powers) was completely erased after her crystal was destroyed by Clark in the Fortress of Solitude. She woke up in Detroit with no memory of who she is or her origins. Her memory and powers were restored by Jor-El in the Fortress, but she didn't remember anything that had happened while she had amnesia.
• In Season 8's Abyss, Jor-El selectively removed the memories of Chloe Sullivan that had to do with Clark's origins and powers.

Notes

• Lex has learned about Clark's powers five separate times. Each time, he has somehow lost that knowledge or disappeared.
• Kara has had total amnesia once, while Clark has had total amnesia twice. For both of them, their amnesia was to the point where they did not know their names and were unaware of their powers (in Kara's case, her amnesia happened at the same time that she lost her powers).
• After Kara lost her memories, she only wore white with the exception of the diner uniform she wore in Fracture. After Kara regained her memory, she immediately began wearing red and blue again.
• After Lex lost his memories due to Tess' neurotoxin attack, he was also shown wearing a white suit. (Finale, Part 2) He was normally shown wearing purple or otherwise dark clothing.