Bill's odd and worrying thoughts seem to make sense in the second film when we find out almost all of Bill's relatives on his mother's side had at least one psychotic tendency like strangling rocks in a religious fit or smashing imaginary animals with a hammer, with his maternal grandmother having had it the worst (she fantasises over killing Bill for no real reason and rubs the heads of dead cats on herself so "the fish can't smother her brain") Extreme mental illness is in Bill's blood. The implication in it's such a beautiful day that some of these stories were purely the result of Bill's decaying mind makes this even worse, as we never find out which ones were real.
"Genetics is pretty messed up."
At first, the stick figure animation is just another example of Don Hertzfeldt's unique style: pretty much everyone has a simple circle for a head and a couple dots and a line for a face. But in the third film, the simplistic art style (coupled with occasional bits of live-action footage) suddenly has horrifying implications when the doctors start showing Bill photos of people and asking him who they are to help assess his memory loss. The Narrator remarks that Bill doesn't recognise them because to him, "they all look the same". They're not stick figures because that's how they're drawn- that's how Bill sees everyone.
