Maws are similar to Horfs, but will slowly float towards the player in addition to shooting blood at them. They also bounce back a lot more from the player's shots, and sometimes unpredictably so. In The Caves they are frequently encountered on their own. They often also spawn from Mr. Maws.
There is a red variant of these that have their mouth stitched shut, and so can only float towards the player, albeit at a faster speed than regular Maws. They explode into four bullets in a + pattern when killed.
A "psychic" variant also exists which fires homing tears at Isaac. Both their eyes and mouth are stitched shut, and they have a large, ghastly eye on their forehead which burns with purple flames and cries blood (this appearance is similar to Isaac with the Spoon Bender item.) They behave exactly like other Maws, but fire homing shots and have more health than normal Maws, thus making them a much greater threat. They also have a Eternal Fly which orbits them, providing extra protection.