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Despite their appearance not resembling to a worm, they are still related to the Round Worm and its other related variants.
They burrow and surface like all other worm enemies but slightly slow. If Isaac is in their line of sight, they will usually spawn a Dart Fly, but they may rarely shoot a blood shot. Ulcers take more time to burrow after they surface, making them more vulnerable to attacks.
- If Isaac is far away from them, Ulcers will not spawn a Dart Fly or shoot. Same apply to other worm variants.
- An ulcer is a break in the membrane of an organ and hinders it from performing its normal functions.