In Worms, sheep are used as suicidal explosives. The helpless animals run in the direction they're released in, turning around only if their path is blocked. Seeking freedom, their plans are inevitably thwarted when the automatic timer runs out or a player triggers their detonation, bringing their life to an end.
In Flockers, a Lemmings-style puzzle game from Worms-developer Team 17, the sheep have had enough. Rather than continue this hopeless existence, they make a break for it.