A pit bull getting a walk in Old City yesterday slipped loose of its collar and attacked a horse.

Kelly, a light-brown pit bull mix, jumped up and latched onto the horse's underside and leg about 2 p.m. outside the adoption center of the Philadelphia Animal Welfare Society, where the dog was being housed, said Allison Homer, PAWS' assistant manager.

"She just got really scared," said Homer, 24. "She's had a rough life, and she gets easily rattled."

Kelly was outside and about to go for a walk with a PAWS volunteer when the Philadelphia Trolley Works carriage pulled up next to her at 2nd and Arch streets, next to the adoption center. Homer said the dog slipped out of her collar, ran toward the horse and latched on.

Melissa Levy, 37, PAWS executive director, said the carriage driver tried to get the horse to move to shake off the dog.

Kelly ended up getting caught under the horse before Homer ran outside and clapped and called the dog's name to get her to let go.

Levy said the horse was taken by trailer to be examined by the owner's veterinarian. The horse was expected to recover.

Levy said that Kelly was brought to PAWS in April by someone who witnessed the dog being thrown out of a moving vehicle on Kelly Drive. PAWS has been trying to get Kelly adopted for the past two months.

Michael Kates, the vice president of operations for Trolley Works, did not respond to requests for comment.