CSI: Crime Scene Investigation, Season 10

Doc Robbins:
C'mon, you're not gonna ask me about the zombie thing?

Nick:
Well, you're obviously eager to tell me.

Doc Robbins:
Well, damage was predominantly on the right side of the brain to the neo-cortex which controls thought, language and reason. It was almost completely destroyed. But the paleo-cortex which lies beneath it remained intact. The paleo-cotrex controls learned instinct and rituals. Which explains why the victim was able to brush his teeth and eat his breakfast without noticing that he was bleeding.

Nick:
They never seem to get that right in zombie movies.