I can think of a very good reason why animals would respond better than humans - because they don't know how to dis-believe, as we do.

Only us cynical human beings would insist that nothing is real without evidence and proof. In fact, our cynicism could be seen to be interfering with the healing process.

Because their belief (or lack of) played no part in the results, there was no placebo effect.

You might want to conclude that the response is a result of kind humans doing things. I guess that depends on what sort of response you are talking about.

Or you could choose to drop the cynicism for a moment, and allow for the possibility that the treatments actually worked.