So the Warners have all said more than once that they're not puppies. (They're also not cats, or bunnies, or fleas and so on and so on. Look up the song What Are We? for more details.) But there are quite a few instances where they do act like puppies (Wakko even more than the other two siblings, but they've all had their moments).
I've got this hc that the Warner boys find it relaxing to be scratched on the tops of their heads or behind their ears like puppies. Wakko has to take his hat off first before it will work.
Maybe they thump their legs when people scratch their ears, idk. Or maybe they purr like cats bc after all they're not dogs, no need for them to be too dog-like.
Why only the Warner brothers and not Dot? Because Dot's had her ears pulled up into a ponytail since the 30s, and tbh when I had long hair it hurt just to wear my ponytail to bed, even without other people messing with it.
(The video in the media is a few of the moments from the 2020 series of Wakko acting like a pupper. I wasn't able to find a video of my favorite puppy moment from the older series, which this hc is partially based on. It's in the sketch 10 Short Films About Wakko Warner, Wakko volunteers at a nursing home by basically being a therapy animal to the elderly, it's so friggin' cute! 🥺💙💙)