Got out of my car after work yesterday, right at dusk. Big commotion in a tree at the edge of the yard. Up about 40 feet were two squirrels fvckin around. Next thing, a dark grey oblong object is falling, straight down, then WHAP! Smack on to the layer of ice over the snow. I'm like "o, that fvckers dead". Three seconds later, there's a squirrel climbing back up the tree. I figure that was his buddy. I scale the ice hill to the spot of impact (ice was just about strong enough to hold my weight), and there's a divet about 2 inches deep and 6 inches in diameter. Fvcker broke the ice layer, and lived. Good thing, I wasn't in the mood to scoop up squirrel guts.
Bottom line, those fvckers ain't too smart. Resilient, maybe. Smart, not so much.