That "poof on top" is called a crest. Crests can be large like in the case of the Polish or small like in the case of the Legbar. All crests are caused by a deformity called a "vaulted skull"-the deformity causes a lump on the skull that has big holes in it, and it makes the nostril area slightly deformed as well. This vaulted skull commonly causes brain issues such as seizures, fainting, and water in the brain, but it is still bred into many breeds because of the adorable crest it makes on the chicken's head. But do not worry, not all chickens with vaulted skulls get brain problems.poof on top?