Bavarian Bunny
Wise Old Thumper
Looks like dock seeds, but it's hard to tell on that photo. Are there any leaves on the stalks or is it just seeds? I think rabbits don't like dock, because it is too bitter, but that may be true for certain dock species only. Dock seeds can be poisonous to animals, the whole plant contains oxalate, like rhubarb. Oxalate can damage the kidneys, I think.