Little Johnny is at school, and at the end of the day the teacher
ask the students to bring one electrical appliance, for "Show & Tell"
the next day. So the next day every kid has something.

The teacher asks Wendy: "What did you bring?"
Wendy: "I brought a Walkman."
teacher: "And what is it for?"
Wendy: "You can listen to music with it!"
teacher: "That is nice Wendy, and what did you bring Kenny?"
Kenny: "I brought a electrical can opener, it opens cans, miss!"
teacher: "Well done, Kenny, but I see that Johnny didn't bring anything!"

Johnny: "Yes, I did. It's in the hall."

The whole class looks out into the hall.
teacher: "WHAT IS THAT, JOHNNY?"
Johnny: "It is a heart/lung device, they use it in hospitals to keep
your heart going!"
teacher: "And what did your father say about it?"
Johnny: "AAAAAAAHHHHHHHHHHHHHH!!!"