One of the claims for the effectiveness of various alternative medicines, especially homeopathy, is that they work in animals. In humans, the usual explanation for any benefits is the placebo effect: you get better because you think you're going to. This is why double-blind testing is so important in drug trials. However, surely the placebo effect shouldn't work in animals?
First of all, Homeopathy cannot work. It really is just water. If you have to start rewriting the laws of physics to explain how your treatment works, that's a pretty good clue that maybe it doesn't. This makes me instantly suspicious about claims that it is effective in animals.
It actually appears that animals aren't as immune to psychological effects on their health as one might first think. For a start, dogs can fake illnesses. Faking a limp is quite common, and dogs can also manage nausea or diarrhea with no physical reasons. The reason is simple: when they are ill, they get special treatment, nicer food and more fuss. Being ill clearly pays. So if an animals psychology can cause physical symptoms, it's quite likely that they are amenable to the placebo effect. Claims for homeopathy certainly all seem to be in the more intelligent animals, such as dogs and horses, rather than, say, in mice.
In fact, the main way homeopathy would work in animals is placebo by proxy. The owner expects the animal to recover, and treats it as such. Animals are very good at picking up on such cues, and the effect would be much the same as in humans. Only a proper, double-blind trial would show the effectiveness or otherwise, and I know which way I'd vote.