The English Language and Digestive Illness

A query about spelling: The plural of scarf is scarves, but the spelling doesn’t change when you’re talking about the verb scarf, meaning “to eat quickly.” You would say, “When my dog is hungry he scarfs down all his food,” not “scarves down all this food.” Why would the letter change only in the noun? Is it because the verb scarf is slang? Doesn’t the switch from “F” to “V” happen in order to make the word easier to pronounce? The similar sounding dwarf can pluralize to dwarves (though I think some people might use dwarfs), but it stays as dwarfs as a verb, as in “The new building dwarfs the ones around it.” But then again, morph stays the same — or would, perhaps if you were speaking about Power Rangers and counting transformations: “one morph, two morphs.” Does it stay the same because its “F” sound is represented with something other than the letter “F”? Or am I approaching this completely wrongheaded?

By the way, I arrived at this mystery by trying to figure out what the correct plural for barf would be, as in “one barf, two barfs.” Barves? I mean, I know it’s not, but I kind of wish it were barves.