One way to camouflage yourself in a tree it to look like a tree, i.e. turn green and barely move. Sloths grow algae in their fur to handle the "turn green" part of the equation. Our guide said that other plants and insects live in the fur and that a sloth is basically a "mobile ecosystem".
This one looks like it is trying to remember something, perhaps the name of that neighbor sloth it met at last year's Christmas party.