A prostethtic makes all the difference when going for gold. Biomechanics can help pick up slight imbalances in a runner's form, so they can yield a better run time.

Ellen scare-pranks the actress Julia Roberts by hiding in her bathroom.

When Chandler needs to visit a tailor, Joey suggests his family's one. But things get out of hand.

The Doctor creates a doppleganger of himself to carry out his plan and empathize with the man-made dopplegangers.

Amy uses active listening skills to pretend to be interested in Sheldon's opinions on Xbox vs. Playstation.