Bored bros have been setting their farts on fire for decades with nary a burnt backside, but it’s not always harmless fun. A surgical patient in Japan suffered severe burns after a laser-ignited flatus set fire to the surgical drape around her, revealing the dark side to uh, getting lit.

Japanese news outlets report that a patient in Tokyo Medical University undergoing an operation on her cervix suffered serious burns to her waist and legs after a surgical laser set fire to an unexpected gas leak. The official report notes that the patient’s intestinal gas was strong enough to cause the fire to reach the surgical drape around her, suggesting that her near-fatal fart was particularly dense with highly flammable hydrogen, hydrogen sulfide, and methane gas.

As one might deduce from the odors of different farts, their gaseous compositions can vary widely, depending on what food a person ingests and what bacteria are available to break it down. As these bacteria digest your meal, they burp out gaseous byproducts, which are ultimately what collect in the intestines and eventually force their way out of your backside. Most of these gases are benign: Nitrogen, carbon dioxide, and oxygen, which together make up the majority of the average fart, are not flammable. It’s likely, however, that the unfortunate Japanese patient contained higher-than-usual levels of highly flammable hydrogen and methane-based gases in her gut before she headed to the OR.

Methane-rich farts, though not the only flammable type, aren’t thought to be especially common, but eating certain foods can increase the amount of the gas that ends up being released. Cruciferous vegetables, like broccoli, cabbage, and kale, contain high levels of methane that may be burped out if you’re lucky (or unlucky) enough to have bacteria in your gut that can break them down.

Incidentally, methane gas burns blue, which is why the rare but highly-sought-after “blue angel” and “blue dart” farts exist.

Farts that are richer in hydrogen, in contrast, tend to burn yellow or orange. In general, setting farts on fire is not recommended because it pretty much creates a direct line of fire from the lighter to the inside of your rectum. If you’re going to do it, it is probably safest to keep your pants on — though those, obviously, may catch fire as well. Avoiding open flames in general is a good idea if you’re especially gassy, because an ill-timed ignition event — say, for example, the sudden emergence of a surgical laser — could end in utter disaster, especially if your personal gas is plentiful and has had time to diffuse.