The next time you lose your keys, check your butt. They might be in there.

Because besides being fun to ogle and rent out as ad space, the human derriere has an extraordinary capacity to store things. It's like nature's little knapsack. Just don't expect to easily retrieve your belongings.

"Rectal foreign bodies," as they're known in the medical world, come in all shapes, sizes and degrees of embarrassment. Sometimes they're the result of a prisoner's smuggling attempts gone awry, but they're more often caused by sex fiends getting a wee too enthusiastic in the sack.

From household items to explosive devices, keep reading to to see the craziest junk medically removed from people's trunks.

Glass Bottle
A 60-year-old man was admitted to the hospital with a case of perforation peritonitus (aka a torn-up tush), which doctors believed was a rare spontaneous occurrence. Fast-forward a year later, when the same man comes in with stomach pains and difficulty walking. Upon X-ray-ing him, they found a huge glass bottle in his rectum and realized that the guy doesn't have a magically exploding butt; rather, he just likes stuffing objects in it. The docs surgically removed the bottle, and the patient made a full recovery.

Vibrator and Salad Tongs
Horniness and pride are a terrible combination, as exhibited by this patient who was too ashamed to seek medical attention after a vibrator became lodged in his you-know-what. Instead, he tried to fish it out himself with a pair of salad tongs [insert salad-tossing joke here], which followed the same path of the vibrator and also got lost in his seemingly enormous colon. He wisely chose to swallow his pride and took his ass to the hospital, where doctors removed the vibrator and tongs, which hopefully did not return the silverware drawer.

Concrete Enema Mix
First, a quick lesson: A klismaphiliac is someone who is sexually aroused by enemas. A poor decision-maker is someone who shoots concrete mix up his butt. Both of those terms could describe a certain 20-year-old man who was taken to the E.R. after his boyfriend poured a batch of wet cement though a funnel into his pooper. Doctors were able to deliver the "stony, hard mass," which is that anus-shaped rock you see on the right -- and the one you'll see later in your nightmares.

Live Ammo
A WWII veteran was "treating" his hemorrhoids by shoving the piles back inside him using an artillery shell from one of his war guns. So thorough was he in the hemorrhoidal reversal that the veins and the shell ended up inside his body -- which, in turn, ended up inside a hospital. Assuming the explosive wasn't live, the doctor was about to go in for it. But, just to check, he quickly asked, "This shell is spent, isn't it?" To which the old man with the bullet up his ass replied, "Oh, no, there's enough ammo in that shell to blast a Messerschmitt out of the sky." The bomb squad was called in to build a lead box around his butt and defuse the shell before docs removed it. They all walked away unscathed, except for the patient, who still had a raging case of hemorrhoids.

Peanut Butter Jar
The most notable part of this case study isn't that a 65-year-old man arrived to the E.R. with a peanut butter jar trapped in his rectum (although just try not to clench your butt cheeks while picturing that). It's his explanation of how it got there: The elderly man claimed that while washing his dog in the shower, he slipped and fell on the jar so hard that it passed right through his anal sphincter. Physics and biological impossibilities aside, there are a lot of holes (heh) in his story: Like why was he naked while bathing his dog? And why is there a jar of peanut butter in the bathroom? Perhaps he has grandchildren, and they're better off not knowing that Gramps gets an erection when he inserts a container of Skippy up his butt. Anyway, who's hungry for a PB&J?