bathroom scale
 

Two youngsters were closely examining bathroom scales on
display at the department store.
"Have you ever seen one of these before?" one asked.
"Yeah, my mom and dad have one," the other replied.
"What's it for?" asked the first boy.
"I don't know," the second boy answered.
"But if grown-ups stand on it, don't go near them for ten minutes.
That thing makes them mad."

Barbara