I can see it all now.
Inquisitive squirrels risk it all and slowly "go nuts" as they investigate the cults of Chipmonkthulhu, Nut-lo-tep, Hastur the Hampster and the black squirrel of a thousand young. Beware the King Fisher in Yellow and the Great Race of Nihm. Seek out the Box Elder Sign to close portals to alternate reali-trees.
Edit: Sanity could be tracked by by a pool of marbles. As you loose marbles (sanity) you gain nuts (insanity). Squirrel mental illnesses could be correlated with different kinds of nuts.
Peanuts = Phobia of Carnies and baseball games.
Pine Nuts = Aversion to air freshners and detergents.
Acorns = kleptomania.
Chesnuts = Phobia of chess pieces, chess boards and checkered patterns.
See, you're getting it. Very good. This the Nuts Meter.