What is "bullheads"

Usage examples of "bullheads".

But two bullheads stood in the way, their horns lowered, and he could do nothing.

That one stepped right off a Satorday Evening Post cover with a string of bullheads, and preserved himself in junk.

That one stepped right off a Sator day Evening Post cover with a string of bullheads, and preserved himself in junk.

She turned away from the battered kerosene-burning stove over which she was frying sliced potatoes and perch and bullheads caught in the Illinois River, half a mile away.