"Show and Tell Time" joke

The teacher asked her students to bring one electrical appliance for Show and Tell and the following day, each child had brought something.
"What did you bring, Lucy?" asked the teacher.
"I brought a walkman," Lucy said.
"And what it is for?" the teacher asked.
"You can listen to music with it," Lucy explained.
"What did you bring, Eric?" the teacher asked.
"I brought a 'lectric can opener. It's for opening cans," Eric said.
"Very good, Eric," said the teacher.
"Johnny, what about you? I didn't see you bring anything," said the teacher.
"Yes, I brought something. It's in the hall," Johnny replied.
The teacher and all of the students then went out into the hall to see what Johnny had brought.
"Umm, Johnny, what is that?" asked the teacher.
"It's a heart/lung machine. Hospitals use it to keep your heart going," Johnny proudly explained.
"Oh dear! What did your father say about you bringing this?" the teacher inquired.
"He said, "AAARRRRGGGH!!"