"Curious Johnny" joke

Little Johnny was 12 years old and, like other boys his age, was rather curious. He had been hearing quite a bit about "courting" from older boys and he wondered what it was like and how it was done.
One day he asked his mother who became rather flustered. Instead of explaining things to Johnny, his mother told him to hide behind the curtains one night and watch his older sister and her boyfriend. This he did.
The following morning, Johnny described everything to his mom. "Sis and her boyfriend sat and talked for awhile then he turned off most of the lights. He then started hugging and kissing her."
"I figured Sis must be getting sick because her face started to look funny. He must have thought so too because he put his hand inside her blouse to feel her heart just like the doctor would do. He was not as smart as a doctor because he seemed to be having trouble finding it."
"I guess he was getting sick too because pretty soon both of them started panting and getting all out of breath. His other hand must have been cold because he put it in her skirt. About this time Sis got worse and began to moan and groan and squirm around and slide down towards the end of the couch."
"This is when the fever started. I knew it was the fever because Sis said she felt real hot. Finally I found out what was making them so sick. A big eel had gotten inside his pants somehow. It just jumped out of his pants and stood there, about 10 inches long, honest. Anyway, he grabbed it in one hand to keep it from getting away."
"When Sis saw it, she got real scared, her eyes got big and her mouth fell open and started calling to God and stuff. She said it was the biggest one she ever saw... I should have told her about the one down at the lake."
"Sis got brave and tried to kill the eel by biting its head off. All of a sudden she made a noise and let the eel go. I guess it bit her back. Then she grabbed it with both hands and held it tight while her boyfriend took a muzzle out of his pocket and slipped it over the eel's head to keep it from biting again."
"Sis lay back and spread her legs so she could get a scissor lock on it and he helped by laying on top of the eel. The eel put up a hell of a fight. Sis started groaning and squealing and her boyfriend almost upset the couch. I guess he wanted to kill it by squeezing it between them."
"After a while they both quit moving and a great sigh came forth. Her boyfriend got up, and sure enough, the eel was dead. I knew it was dead because it just hung there limp with some of its insides hanging out."
"Sis and her boyfriend were a little tired from the battle but they went on courting anyways. He started hugging and kissing her again. By golly the eel wasn't dead after all. It jumped straight up and started to fight again. I guess eels are like cats with 9-lives."
"This time Sis jumped up and tried to kill the eel by sitting on it. After 35 minutes of struggling, they finally killed it. I knew it was dead because I saw Sis's boyfriend peel its skin off and flush it down the toilet... "