'ER's' animal antics: Animal guest stars

Human stars weren't the only ones who entered the doors of "ER" over its 15 years.

Animals may not have gotten their own director's chair or trailer (except for the horse), but they always stole the scene -- whether they were fuzzy, hoofed or even gilled.

Check out the handful of animals that figured out how get the hospital staff's attention without filling out all that paperwork.

-- Hanh Nguyen, Zap2it.com