[[Hat Guy is sitting on a chair, the Normal Guy is standing next to him. Across the street another man is coming from a building.]]
Hat Guy: There's a certain type of brain that's easily disabled. If you show it an interesting problem, it involuntarily drops everything else to work on it.
[[The man across the street is about to enter a crosswalk]]
Hat Guy: This has led me to invent a new sport: nerd sniping. See that physicist crossing the road?
[[Hat Guy holds up a sign]]
Hat Guy: HEY!
[[There is an image of a grid with resistors on every connection, two nodes a knight's move apart are marked with red circles.]]
The sign reads: On this infinite grid of ideal one-ohm resistors, what's the equivalent resistance between the two marked nodes?
Physicist on the street: It's... Hmm. Interesting. Maybe if you start with... No. Wait. Hmm... You could--
[[A truck is zooming past, apparently where the physicist just stood]]
<<FOOOOM>>
Normal guy: I will have not part in this.
Hat Guy: C'mon, make a sign. It's fun! Physicists are two points, mathematicians three.
{{Alt: I first saw this problem on the Google Labs Aptitude Test.  A professor and I filled a blackboard without getting anywhere.  Have fun.}}