Ever rub your hands together and notice that they warm up? That's friction, the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. Friction creates heat which can create a small flame if on a dry surface. In fiction however, particularly animation, friction can cause one to burst into flames. This is usually Played for Laughs and is often caused by a character's own stupidity. In superhero fiction, characters with Super Strength might do this. Compare Playing with Fire, when this trope is weaponized.