"비누는 왜 먹고 있니?"
Translation:Why are you eating soap?
Notice that the topic marker 는 is being used, and not the object marker 를. This is one of those sentences where the topic is NOT the subject of the sentence (so it's not "Why is the soap eating [something]?"). To translate literally, this sentence could be something like: "About the soap .... why are you eating it?"
I've noticed a lot of frustrating problems in this course with "a" versus "the" in the English answers that are expected. Both are correct translations of the Korean in most cases, but lots of the questions only seem to accept one or the other (such as this one being marked as wrong when you translate it with "the soap" at the end), and there's no way to know which one is expected without failing the question first. The English for Korean speakers course consistently expects 그 in front of nouns that have "the" in English, and while I'd disagree that this is always necessarily implied by the English, it's at least consistent and predictable. Can we perhaps get a similar level of consistency with articles employed here? Or failing that, both "the" and "a" added as valid answers on a consistent basis?
Even if this were a beta curriculum, the Korean course on Duolingo is simpky one of the lowest qualities I've seen. We shouldn't need to flag the wrong stuff for the creators to get to this still-below-average course. Duolingo needs to hire real teachers with experiences. The users need to flag bugs, not the course itself.