A very religious parrot

A preacher is buying a parrot. "Are you absolutely certain it doesn't swear?" asked the preacher. "Oh absolutely. It is a very religious parrot," the storekeeper assured him. "Do you see those strings on his legs? If you pull the right one he'll recite the Lord's Prayer. And if you pull the left one, he'll recite the 23rd Psalm."
"That's wonderful," said the preacher. "But what happens if you pull both strings?"
"I fall off my fuckin' perch, you goddamn shit-for-brains," screeched the parrot.