Some of a them will eat anything and everything, including many things that aren't good for them. Most will eat wood, which is why you don't want to build fences/barns with wood. Maintenance nightmare! Some like to suck air, a nervous habit... If you go to a sale and see one with a strap around its neck, avoid that one! I personally think it might be related to weaning too early, but can't verify that... Just my opinion (I also think that weaning too early may help cause humans to become addicted to smoking (besides the addictive drug nicotine)...Wow that's really interesting. Is that common for horses to want to eat the bedding?