@Mr_NutterButter this is quite the layered joke. Google says it translates out to "guroman" and with my limited knowledge of Japanese and the context of this meme... Here's my best guess.

Guro (the first two characters) is basically "grotesque," and a slang term for vagina is manko (sort of translates to "pussy" in English). The last two characters seem to be related to some sort of filled baked good that can sometimes resemble a vagina. So it is likely some sort of layered pun relating to a pussy (another word for cat of course) looking at a pussy (vagina, manko) and thinking "that's not a cat, that's just a disgusting steamed bun!"

Although you can pretty much gather that from just looking at the image even if the text wasn't there, the text adds a bit of a punny layer to it if you know some Japanese and their food. Or if you know how to search around for those things. I'm not sure if cats being pussies actually translates over to Japan or if that's just an English thing, so perhaps you need to understand a little bit of English to get the "full" joke or maybe that wasn't intended in the first place and the cat is just there because cats are funny or something.

I could be wrong but that's my educated guess.