This guy goes to a pet shop to buy a parrot. There he sees a parrot with a red string1 tied to its left leg and a green string tied to its right leg. He asks the owner the significance of the strings.
　　“Well, this is a highly trained parrot. If you pull the red string he speaks French; if you pull the green string he speaks German,” replies the shopkeeper.
　　“And what happens if I pull both the strings?” our curious shopper inquires.
       “I fall off my perch2 you fool!!” screeches3 the parrot.
 

1． string n． 线，细绳
2． perch  n． (鸟类的)栖木
3． screech  v． 尖叫