Eva Head can also mean the mind set one must be in to watch Eva and atempt to understand what is happening. It is simlar to idea of putting on one's "thinking cap"
2nd Guy: Oh no! He's gonna get Eva Head. We probably shouldn't talk to him for a few months.
2. 1st Guy: We got 13 hours to kill, wanna do a marathon?
2nd Guy: Alright, time to put Eva Head.