Mine recommended 'whom is a crab eating?' Duolingo seems very fond of ungrammatical answers XD
That is a perfectly grammatical sentence. However, it means that a crab is eating someone, rather than (as most would infer from the sentence) that someone is eating a crab.
I don't think the correction I got ("Whom does a crab eat?") is proper English...
It is, actually. It just means that the crab is eating someone rather than that someone is eating the crab. I don't know why this would be the preferred translation, as usually the subject comes first in these constructions, thereby implying that someone is eating the crab, not the other way around.
How to say. Whay does a crab eat? Can anyone explain. I thought thats correct.