The Blood Blisterpod is a small purple sweet, invented by Fred and George. Half of it causes a nosebleed. The other half of the sweet stops the bleeding.
Fred accidentally gave the wrong half to Katie Bell during a Quidditch practice to stop her nosebleed, with disastrous results (OP14).
Seems to have a very similar effect to Nosebleed Nougat. Both sweets have two ends, one causing the nosebleed, the other cancelling it.