I guess it's weirder for a tile to flip between two images than it is to flash an N.
No. Absolutely the opposite. If I'm in proper rogue/nethack mode, letters become creatures. But if I'm in a visual sprite mode an N looks *extremely* wrong and jarring.
Flipping between two images keeps the same "mode" engaged, while flipping between an image and a letter makes me want to claw out my eyes.
I disagree, but that's what options are for.
but... I don't get it
what's the point in making it flash AT ALL if it's already showing a zombie graphic?
For clarity, it's entirely possible to have a zombie graphic for all races.
What the hard-coding of the flashing tile does is force the flashing between the specific zombie-of-that-race tile, and a generic undead tile.
So, even without flashing, we can see things like this:
Which can be easily recognized as zombies without having to flash to some other tile.
It's getting more and more the case, what with several hundred types of creatures all loaded onto the same letters, that graphics are actually getting much easier to recognize creatures than having to guess whether "s" means rattlesnake, rattlesnake man, copperhead snake, copperhead snake man, slug man, snail man, sparrow man, skunk, skunk man, satyr, siamang, strangler, helmet snake, giant sponge, sponge man, frill shark, squid man, spiny dogfish, and maybe some other things I didn't get in a quick browsing. (And yes, there are color variations, but most of those are either gray or brown, anyway.)