Like Chickat said, it's very diluted, it just smells bad and will sting a bit -like if u get soap in your eyes (it's a wide spray and I'm not a very good shot, I don't think I've ever got one directly in the eyes!). It doesn't cause any injury. Kicking, hitting, and killing them are much more "cruel"! With this technique, they learn after 1 or 2 squirts that they need to stay away from me. It completely diffuses their "cocky" behavior w/ me and all the other humans that are in the barnyard. I don't hv to worry anymore about my kids and grands and ranch hands getting attacked.
My dad used this technique to discourage a dog who chased his car every morning on the way to work. He was afraid that one day the dog would bite his tires and die. He used lemon juice instead of ammonia because that was what was available. Broke the dog of chasing him. Dog still chased other cars though.