The worst are the little dogs on 30-foot leashes, usually attached to oblivious owners. There was a recent thread on the Paceline forum from a guy who got clothes-lined (dog on the left side of path, owner on right, thin cord stretched out across the path). Poor guy didn't see the thin leash until it was too late, went over the bars, and broke his collar bone badly. He was much more understanding that I would have been.