There is a palpable series of definite events in “Caveat” that one can lay out explicitly, even if the film takes place in a surreal dreamspace. We’ll have to set aside the eerie, haunted house for the time being, and first lay out what seems to be definite. A lot of these facts are laid out in a montage at the end of the film.
Moe and Isaac were once friends, and Moe seemingly had a contentious relationship with his brother, Olga’s father. A short while ago, Moe hired Isaac to lure Olga’s father into the house’s basement, hoping that the claustrophobia would drive him mad and lead to his suicide. Isaac, however, had a change of heart, and decided not to go through with Moe’s plan. The basement door was unexpectedly locked. Moe became angry at Isaac’s inability to finish the job, and he pushed Isaac off a balcony. Isaac, who had arrived drunk, hit his head and became afflicted with amnesia. In the present day, both of Olga’s parents are dead in the house. Her father’s body is in the basement, and her mother’s corpse is hidden in a wall.
It’s never actually explained how Olga’s mother and father died. One might be able to infer that Moe killed them, but that’s never stated explicitly. One might also feel that Olga killer her parents, and that their ghosts now stalk the house, seeking revenge. Regardless, Isaac is not guilty of any crimes. Indeed, the eerie rabbit toy seems to be there as a protector, to warn him of danger, be it from ghosts, Moe, or Olga herself.
It’s also never explained how the rabbit toy (which looks like it could be a cousin to the deranged-looking rabbit from “Donnie Darko”) can sense danger, or why it drums when danger is near.