The following animals are funny when...

Gerbils, especially when seen lifting weights.
Platypus's, especially when used out of context.
Beavers, in any number of jokes involving the word "stuffed."
Giant Ground Sloths, in almost any context.
Sheep, especially the vampire variety. Or when discussing David.
Howler Monkeys, when discuss screechy people.
Chimps, when dressed as 80s action film heroes, when wearing tutus and riding tricycles.
Donkeys, when wearing sombreros and walking into easily visible walls.
Bunnies, when commenting on the mighty Esquilax, a lion with the head of a rabbit and the body of a rabbit.
Circus Folk, while commenting on things with small hands which smell of cabbage.
Pooh-Bears (fictional), upon a) meeting someone named "Winnie" or b) when someone gets their head stuck in a pot of honey.
Cows, almost anytime.
Ducks, when speaking in British accents.
Penguins, when shooting out of icy water, when waddling around Antarctica, or when trying to kill batman