When cowboys would be sitting on their front porch or at the local bar outside talking with nothing to do, they would sometimes take their pistols and shoot at cow pies or horse poop lying in the street or across the way.

This became known as “shooting the shit.”

When they were hunting fur, a hunter might point out what they thought was a beaver or another valuable small animal, but upon further inspection would sometimes say, “Aw, that’s just bullshit.”