Lynda Barry

Sometimes it's even hard to tell the difference between a tic and a compulsion. But while tics stem from an urge in a specific part of the body - either completely unconsciously or through a premonitory sensation that's satisfied only by the tic - OCD bubbles up as conscious thoughts in the mind.

Listening and hearing are two different things, and acting is comprehending what the person is saying, thinking how it makes you feel and responding. That's the key to really honest, truthful, compelling performance.