Jerry is related to Dr. Dolittle
He is insane but the animal voices are real.- Semi-confirmed. His insanity 'gave' the voices to the animals and severed heads of his colleagues.
Jerry was feeding the corpses to his pets
Jerry stores the chopped-up bodies in small Tupperware containers. Why? We know that the things his sees are not accurate, and we see him frequently feeding his pets. What better way to get rid of the meat than feeding it to his pets?- Confirmed. His 'world' is full of hallucinations.
Jerry's mother really did see angels
Bosco and Mr. Whiskers are the literal angel and devil on Jerry's shoulders. This is all a prolonged game between God and Satan, e.g. Job, to see if Jerry will take the moral path.