In English, there are true verbs and there are "verbals". Verbals are words that "were" a verb, but are no longer acting like a verb. The verb "to do" looks like this in its present progressive tense: "am doing", "is doing", "are doing" This is the true verb in the sentence. However, a verb may be used as a noun and still have the ending "-ing". We call this a gerund: "Eating fast food is not a good long-term choice." Here, the verb is the word "is". When we ask "WHAT is not a good long-term choice?" the answer is "eating (fast food)". The word "eating" is a gerund. Here it is acting like a noun. It is the subject of the sentence. Here's another example: "I don't like eating fast food." The verb is "do(n't) like". The subject is "I". When I ask, "I don't like WHAT?" the answer is "eating (fast food)". It is acting like a noun. It is the direct object of the verb. In English, we also have something called the present participle. This is a word that ends with "-ing", but which is now acting as an adjective or adverb: "Eating fast food, you will gain weight quickly." Here, the true verb is "will gain". The subject is "you". When I ask "You will gain WHAT?" the answer is "weight". The word "weight" is a noun and it is the direct object of the verb. The word "quickly" is an adverb, telling us HOW the "gaining" will happen. So what about "Eating fast food"? The word "Eating" here is a participle. It is acting as an adverb (the whole phrase is), telling WHY the gaining will happen. In the sentence given ("What are you doing eating fast food?"), the word "doing" is part of the true verb. It is in the present progressive ("are doing"). The word "eating" is NOT a verb here. It is a verbal. The question is, WHAT kind of verbal is it? [cont. below]

I don't know the proper name of this synthatic paradigm, but, in Portuguese, we would call it a 'Reduced sentence from gerund'. It means that this phrase at full lenght could be: 'What are you doing when eating fast food?' 'What are you doing while eating fast food?' etc. i.e. With a conjunction. You may remove the conjunction if you wish to get a faster pace or if you wish to supress the synthatic value of the conjunction (time, cause, consequence, etc.). So, note that, without the conjunction, the phrase means something different. It is not asking about the action you are doing while or when you're eating, for example. It is asking why you are eating. Hope it helped you. =]

There is only one continuous verb form in the sentence "What are you doing eating fast food?" The present continuous form of the verb do "are doing". "Eating fast food" can be considered a gerund phrase. In case you are not aware of exactly what a gerund is, here is a good explanation: http://www.englishclub.com/grammar/verbs-gerunds_1.htm Discussion: Thiago stated that there might be an ellipse of a conjunction (more likely a preposition). What are you doing "by" eating fast food? retains the full meaning of the sentence. However I don't thing that we need to look for a "reduced gerund" or ellipse. Eating (fast food) is the object gerund of the verb "are doing". In the sentence "What are you doing eating fast food?" "what" in this context does not function as a pronoun but more as an interrogative adverb that together with the whole phrase " What are you doing" means "why or to what purpose" are you eating fast food? The question is not simply asking if you are indeed eating fast food; it is implying that eating fast food has a negative connotation. It seems to be a carry over from the old English use of "what " meaning "why". Then it implied a negative assertion or comment which seems to be the case here also. For example, What should I tarry? meaning Why should I tarry? There is no reason. What the devil? meaning Why the devil? (What are you doing? by itself has another connotation.) Another example. What are you doing photocopying in here. or Why are you doing photocopying in here. This is fun. Денис

Sorry for the mess. As I said, I didn't know the proper name. And even forgot to explain more, as I should. Told the probable origin, but not what it is now. In Portuguese, we call 'gerund' the verbs, nouns, adverbs, whatever ends with our version of the -ing. Our present participle, as with all of the romance languages, has a different ending. But I do believe Erik completed what I've argued (and did all the hard work). Also, if you consider 'eating fast food' as an adverb (for me, an adverbial clause), you could alter the word order: "Eating fast food, you are doing what?" Albeit the huge semantic change, you would easily see it as an acessory component (which the adverbs are) due to the comma. Like with the earlier example: "Eating fast food, you will gain weight quickly." Again, sorry for the mess and one more sorry in advance if made another now. I'm really willing to help. =]

Two arguments could be made: 1. "eating (fast food)" here is a present participle acting like an adverb; it modifies the verb "doing". 2. "eating (fast food)" here is a gerund acting as a noun; it is an appositive, renaming "What". In either case, we really don't have two progressive verbs. We just have two things back to back that end with "-ing". If you are confused -- that is understandable! English is a confusing language at times! But I hope that helped some.