Of course, spoilers Flowey can do really good face-warps, which may be a side effect of the DETERMINATION. Monsters melt because they haven't got enough physical matter to hold large amounts of it, Humans can effectively use it to change their fate, but... W h a t a b o u t f l o w e r s ? Basically, my theory is that because of the monster dust of Asriel, Flowey can still melt and warp his form, but he has control over it, and uses them to make the facial expressions. I know it's kinda far fetched, as always I mean, but eh, just tryna put it out here before I forgot