See, the wires on those stiff barbecue cleaning brushes frequently come loose and fall out. When they do, they might fall through the cracks and go away. Or they could stick to the next food item that you put on that grill, and then make their way into your body like Trojan warriors in a delicious meat horse. And once they're inside you, they cause immense damage to your digestive system. It doesn't take a genius to figure that extremely sharp metal bit in the guts isn't a good thing.
Complicating matters is that those wires are so fine that they're difficult to detect with x-rays, so doctors are often powerless to explain why you suddenly feel like you ate something with "cowboy" in the name at a Carl's Jr. instead of a healthy grilled chicken breast.
Center for Disease Control
"Well, I suppose we could throw you in an MRI and see what comes out."
Between 2002 and 2014, those little wires sent nearly 1,700 people to the ER, but doctors were often able to remove them right there and then. The less fortunate required laparoscopic (or snakey-arm) surgery to remove the objects, and still-less-fortunate victims had to be hacked open the old-school way. One man nearly died after waiting two weeks to seek medical assistance. When doctors finally got at his insides, they found a penetrated intestine and a blood clot in a lung. So there you go: Never clean your barbecue. If something is dangerous, then the direct opposite of that thing must be safe. Like how bungee jumping is stupidly dangerous, but jetpacks are the statistically the safest method of travel. We assume.