David-42 - actually telling someone they have nothing to worry about can also lead to problems. Simply quoting online text about a condition doesn't prove that it is or is not harmless. I will pipe in on this discussion, being a vet tech I can give an actual account of the problems. As stated before it is not known why the reaction occurs, but dogs that ingest hops, whether they have been boiled or not, is possibly harmful to the pet. Obviously, it depends on the matter of the occurance, size, type of dog, amount of hops ingested, all sorts of variables. I can personally tell that hops have been the reason for 5 canine deaths and 4 more pumped stomachs in 7 years at my ER clinic. To cover the talk about after boiled or not, I have seen both cases, either as said before spread around after boil, or simply the dog got the hops while the owner wasn't paying attention during prep for boil.
But to cover someone elses, question, I have not seen a cat yet with the problem. I would chalk it up to the fact that dogs will eat just about anything, where a cat is usually a little more picky.