Sheep and Scary Coos (thats cows to all you English/Foreigners out there)
Sheep wont get the hell out of the way. Blasting down a bit of fireroad screaming at them to move and get off to the side, and do they? eh no. They have almost been the cause of numerous wipeouts over the years and on two occasions they succeeded. First resulting in a brake lever sinking an inch or so into my leg and the other in casualty with slight concussion.
Secondly is the scary coos. And this is no laughing matter. Have you ever been hiking it through a field with your bike on your back and a load of coos start following you. You turn around and they stop dead then continue to follow you when you start going again. Not nice at the best of times but when the buggers are chasing you and proper running at you with a bull in tow and you have to jump a deer fence to get away from them. Oooof.