Could you kill a horse, barehanded?

[AmadisSB]

Had a long conversation with some friends while golfing the other day and this question came up.

Imagine a large horse in a fairly large outdoor area, some trees etc. You have to kill the horse without using anything, as in, no stones, sticks etc.

I say its very possible for the average male age 21-35 to eventually kill it, they say its not possible unless the human is way above average.

What do you guys think? Also, what animals are impossible for a human to kill without firearms? (knives, swords/shields allowed)