Ulcer Pop is the thirteenth level of the Hospital chapter of Super Meat Boy. The level contains Dust Bunnies, which are enemies that bounce around on walls. The level requires you to go to the top of the room while avoiding the aforementioned Dust Bunnies and small pools of blood.
Once getting to the top you have the choice of getting to Bandage Girl or get the key behind her. If you choose to get the key, you must go back down to get the bandage then go back up to Bandage Girl, do not die or you will have to start over.