When you hit them from behind, they'll turn over. Once you've knocked them over, they won't "reactivate," and you just have to jump on them to eliminate them completely!

These come at you face first. Bump into them, and you'll temporarily "deactivate" them. You'll know this has happened when their face disappears. As soon as they're deactivated, jump over them (avoid the pins!) and hit them from behind! Be careful, since they come in pairs!