@Demomanowar That's over simplifying it quite a bit. Just like purring, it can mean quite a few different things. Hunting, content, stressed. Plenty of reasons to go doing flipping the tail about, just need to learn what means what with your cat. As a side note, the whole wide eyed thing they've got going on in the comic here does tend to come up with cats when they're hunting bugs and such, so odds are pretty good that that's supposed to be a hunting tail wag.
It gets even harder to make sense of them if they're raised with other animals, as they'll pick up those behaviors too. My cats have picked up a lot of dog-like mannerisms, and the dogs the same in reverse. My dog tends to catch people off guard in that he's got a "purr" growl, meanwhile my cat sometimes just sit by me wagging her tail waiting to get invited up. When she doesn't just jump up into my lap unannounced anyway.
TLDR: Animals are weird, you can only ever kind of understand your own pets.