Sometimes it pays to ignore doctor's orders -- no matter how gross the result.
Rachel Franklin and her 7-year-old son, Paul, discovered that after he scratched his knee at a beach near their home in Orange County, California, and it swelled to the size of a large orange.
The doctors suspected MRSA, and told her not to pop the bulging sac of pus, but when the wound turned black, she felt she had to do something.
So she popped the sac and was shocked by what she saw -- a strange round object.
"I thought it was a rock," Franklin said on an episode of "Monsters Inside Me" airing Thursday on Animal Planet. "Whatever it was, it just came out in one piece."
At first, Franklin thought it might be a tiny stone. Closer reflection showed it was something different.
"I realized it wasn't a rock. It has whirls on it," she said. "I turn it over and I think -- I might have laughed out loud. I said, 'Paul! This is a snail!'"
The official name for the snail stuck in Paul's knee is Littorina scutulata. It's a species of sea snail found in tidal areas on the west coast from Alaska to Baja California.
Biologist Dan Riskin, the host of "Monsters Inside Me," said the species of sea snail can easily adapt to different types of environments -- even inside humans.
"The subcutaneous tissue of the human body mirrors the harsh conditions where sea snails usually survive," Riskin said on the episode.
Meanwhile, the Franklins are still shocked by the experience -- at least Rachel is.
"It was too strange to be true," she said. "Paul -- in typical boy style -- just thinks it's cool."