What Lies Beneath

Claire Spencer (Michelle Pfeiffer) moves to Vermont with her husband, renowned scientist Dr. Norman Spencer (Harrison Ford), after a serious car accident that leaves gaps in her memory. Combined with her daughter Caitlin's (Katharine Towne) departure for college, Claire is profoundly affected. Overhearing her new neighbor Mary Feur (Miranda Otto) sobbing one day, Claire is concerned, despite Norman's reassurance, and her worry increases when she sees Mary's husband Warren (James Remar) dragging what looks like a body bag out of the house in the middle of the night.Claire decides to investigate by taking a basket of flowers and wine to the house as a gift. After nobody answers the door she walks around the side of the house and discovers a woman's sandal with a dark stain on it, which she steals. Back on the doorstep, she is surprised by Warren whose surly behavior further arouses her suspicion.Mysterious events begin to occur when Claire is alone in the house pictures fall, doors open and close and Claire witnesses a shadowy reflection in bathwater. Claire is convinced that Mary is dead and haunting her. Desperate for closure, and facing little sympathy from Norman, Claire invites her best friend Jody (Diana Scarwid) to join her for a seance in her bathroom. Claire produces the sandal she had earlier taken from Mary's house and places it on the table. The Ouija board planchette (pointer) does not move, but a candle starts to flicker, then goes out. The dial on the Ouija board then starts to move slowly from M to F.Claire informs Norman of the séance, prompting him to accuse her of going crazy. Meeting Warren, Claire hysterically accuses him of killing his wife, to which Warren responds with confusion before introducing Mary to the pair.Back at the house, a picture falls off the windowsill again. Picking it up, Claire notices a newspaper clipping inside the broken frame. She discovers that it is a partial missing person report for Madison Elizabeth Frank (Amber Valletta). Reading the clipping, she realizes that Madison had been a student at the university where Norman was a lecturer. She decides to visit Madison's mother.Claire takes a lock of Madison's hair from the mother's house, and uses it to perform a ritual that allows Madison to possess her. When Norman returns home from work, Claire, who is still possessed, seduces him. While straddling Norman, Claire's face briefly morphs into that of Madison's. Frightened by the change in Claire's appearance, and by comments she has made, Norman pushes her away. This causes Claire to drop the lock of hair and break the connection with Madison. Claire's memory begins to return and she recalls that she had once caught Norman with Madison. Norman makes a confession: he had a brief relationship with Madison, but realized quickly that he loved Claire too much to leave her, causing unstable Madison to threaten to kill Claire. He then visited Madison to find her dead of an overdose with a letter to Claire. Burning the letter, he pushed Madison's car (with Madison inside) into the lake.Claire urges Norman to contact the authorities, and he agrees to do so. He speaks with the police on the phone, and then leaves to take a shower. Suspicious of her husband, Claire redials the phone and discovers that he had not really called the police. Norman suddenly grabs her from behind and sedates her. He drags her to the bathtub, which is still running, and places her in the rising water. Norman then explains to Claire that Madison was planning on going to the college's Dean about their affair, and he could not let that happen, so he killed her and pushed Madison's car and body into the lake. Expecting Claire to drown, Norman leans over her paralyzed body to give her one final kiss. While doing so, he notices that she is wearing a pendant around her neck. Realizing the pendant is on backwards, he picks up Claire's head to adjust it. Her face suddenly morphs into the corpse-like face of Madison. He is startled and jumps up against a mirror, shattering it. He then collapses and hits his head on the sink, crumpling to the floor.Claire, recovering from the sedative, crawls out of the bathtub and down the stairs. The phone has been disconnected, so she starts to drive somewhere that will have better cell phone reception, passing Norman's body as she leaves the house. Norman, only stunned, chases her and jumps into the truck when she pauses on a bridge. The truck veers off the bridge and plunges into the lake, the same lake into which Norman pushed Madison's car. Norman grabs Claire's leg so that she cannot escape, but Madison's corpse grabs Norman, drags him to the bottom of the lake, and forces him to release Claire's leg so she can float to the surface. Once Norman was drowned, Madison's corpse flashes a creepy smile, pleased that he is dead and that Claire is safe. As if that was a ghost's unfinished business.The following winter, Claire is seen placing a single red rose at the grave of Madison Elizabeth Frank, but not the grave of Norman. The camera pans out and an image of Madison's face is seen in the snow.

Question: What causes gaps in Claire's memory?
Answer: Car accident