Headscratchers / Out of Jimmy's Head

• Just what exactly did Jimmy's mom do while in space to end up having an alien daughter... or should I say who did she do?
  • Jimmy's sister is adopted.
• Then there's the whole thing with the brain transplant.
  • Heck, the injury that results in the need for the brain transplant is this - at best, the injury from getting hit by the train would be Jimmy getting crushed at the speed it's shown to travel at in the film; it would've made more sense for one of his bones to be fractured beyond repair and replaced with the corresponding bone from Appleday's body, resulting in the cartoons appearing in hallucinations.
• As noted on the main page: Appleday's brain in its entirety is transplanted into Jimmy's head, but instead of changing personalities (or at the very least, having an entirely different set of memories), the only difference is that Jimmy can now see the Appleday toons.
  • The movie mentions salvaging Jimmy’s “personality gland”, hence why he’s still himself.