Three nuns used to go to the church from their homes every day.
On the way they would pass a house where a parrot lived.
The parrot would call out three colors every time the nuns would pass by.
They soon realized that the parrot was calling out the colors of their respective underpants.
They tried to fool the parrot by switching positions while walking and even wearing different colored underpants every day, but the parrot was never wrong. Finally they devised a way to fool the parrot by not wearing any underpants at all.
When they walked across the house the parrot spoke out loud, ”Straight, straight, curly.”