Some animals love it, some don't.
For cats, catnip is the best way to get them loaded, it REALLY works.
For dogs, you can blow smoke on them, but not in them. If you do the ear or nose method DO NOT CUP AND BLOW DIRECTLY into the animals, this is very bad for them, rather, just blow it over them. As far as eating goes, DO NOT FEED DOGS MARIJUANA. They have a very differen't digetstion than us. They render the fats and oils much more agressively and faster than humans.
Other than that, it is perfectly safe, but entirely illegal! In all US states, it would be considered illegal to get a cat or dog high, and in fact, you could potentially have your animal taken away and receive jail time for the act.
Cheers!