While it's a bit more sideshow than Big Top, we couldn't resist the urge to put sword swallowing on our list. Because while it may seem like a fancy illusion or even some sort of sleight-of-hand trick, sword swallowing really does involve sticking a blade down your gullet. And that is so obviously dangerous that the Sword Swallowers Association International (SSAI) website includes a whole resource section on the medical complications associated with sword swallowing.
One of those sources is a survey published by the British Medical Journal, which is surprisingly chipper about the health outcomes for sword swallowers. It concluded that swallowers are at risk for harm if they are distracted, swallow multiple swords at a time or aggravate a previous injury — just avoid that, and no problem [source: Witcombe and Meyer]! (To be clear, they had more nuanced advice than that.)
And there's the case of Hannibal Hellmurto, who suffered a seriously frightening stab to the throat in 2012 when he attempted to swallow a lit neon rod. [source: McQueeney]. He ended up with a hole in his throat that put him in intensive care, but the show must go on: Hellmurto is still performing after his recovery.