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Last week, William Shatner sold his kidney stone to the Web site GoldenPalace.com for $25,000. Shatner, who donated the proceeds to charity, convinced his doctors to give him the stone, which was taken out last autumn. Do all patients have the opportunity to keep their excised body parts?

Generally, yes. Many hospitals are willing to return everything from tonsils to kneecaps. After a pathologist examines the removed parts and takes whatever samples are necessary for hospital records, the patients can often walk away with the rest.

Objects that don’t need further scrutiny are the most likely to be given back. Hospitals do often keep kidney stones for analysis, as their composition can give clues about underlying medical conditions. (Stones caused by a buildup of urate, for example, are associated with gout.) A pathologist would be less likely to hang on to gallstones. For one thing, they’re easily visually inspected. And since the entire gallbladder is frequently removed along with the stone, it’s often unnecessary to analyze the gallstone to prevent recurrence.

There are few laws governing medical keepsakes. The California Supreme Court has ruled that living people do not have a right to sue for the return of cell lines removed from them during surgery. It’s unclear what effect this decision has had, though. Many hospitals in California still return tissues, and doctors in other states sometimes refuse requests, even if they don’t have the backing of state law. Some hospitals forbid giving patients their removed pieces, but the Joint Commission on Accreditation of Healthcare Organizations has no overarching regulations in this area.

Just because there aren’t many laws against taking home body parts doesn’t mean it’s an easy thing to do. Most hospitals make patients sign a waiver that cedes ownership of their surgical leavings to the pathology lab. And many teaching hospitals are unwilling to give up potential research samples. To have a good shot at keeping the stuff that’s removed, let your doctor know before the procedure. You also usually have to sign a liability release form on the way out.

Advances in laparoscopic and microscopic procedures mean that many body parts that were once removed whole are now taken out in small pieces. Doctors now use shock waves to break up many stones that might have been surgically removed in the past.Even if the desired piece comes out whole, a pathologist sometimes destroys it while taking samples. He can also decide that it represents a biohazard, though most communicable diseases can be killed with formaldehyde. (Some notable exceptions include hepatitis and prion diseases.)

There can be cultural reasons to bring home your bits and pieces. In some societies, new mothers request that placentas be returned so that they can be buried or, in rare cases, eaten. Some Orthodox Jews believe they need to be buried with all of their parts, including those that have been removed or amputated.

Explainer thanks Dr. Michael Klein of the University of Alabama at Birmingham, Dr. Hal Pinar of Brown University, Prof. Mark Kristal of the University at Buffalo, and Rabbi Joshua Strulowitz of Adath Israel.