Gapers will attempt to walk towards Isaac by taking the most direct route possible. If there is no way to reach Isaac, due to obstacles such as Rocks or Poop blocking the way, they will stand still and avoid moving towards Isaac until a proper route is created.
Frowning Gapers look identical to regular Gapers, but have empty eye sockets that appear closed before they get close to Isaac. When awoken, they have the same head sprite as Horfs. Frowning Gapers move quicker than Gapers and spawn Pacers and Gushers more often.
The look identical to awoken Frowning Gapers, but have green-tinted skin and they are more hunched back.
They shoot IPECAC shots at Isaac at very short range. These shots will kill other enemies in their Area of Effect, but Gurges themselves are immune to their own shots. Like other enemies' explosive projectiles, Gurges' shots can be used to shatter Rocks or open Secret Rooms by making Gurges fire at the appropriate area.
Gurges are somewhat more predictable and accurate in their shots compared to guts and walking guts, because they will always shoot at Isaac's position. However, the timing of their shots is unpredictable. As such, an effective strategy of delivering explosives to a particular area (e.g. Tinted Rock or potential secret room entrance) is to stand still in that position as long as possible before moving to avoid getting touched, in order to prompt the Gurges to shoot their projectiles at you.