I found a meme that says 'I flew in from (wherever) and boy are my arms tired!'. I can understand what's funny about this meme but I can't understand why 'are my arms tired!' is used instead of 'my arms are tired!'. that's not an interrogative sentence, right? why does there have to be an inversion?
After a short interjection of amazement / delight / relief / exhaustion, inversion is not uncommon but only with a limited subset of interjections:
This is discussed in an article by [Andersen and Aijmer in The Pragmatics of Society]:
Subject-Auxiliary Inversion (SAI) is one standard index of the exclamative clause type.... This inversion of standard word order instantiates one type of exclamative sentence and is itself a marker of emotional involvement ....
Occasionally, the inversion-form exclamatory appears without an overt interjection:
- "Am I glad to see you!"
- "Is he one lucky guy!"
It does appear at first glance to be an interrogative due to the subject-auxiliary inversion. However, in this instance, the closed interrogative (yes/no question) indirectly conveys an exclamatory statement, the implicit meaning being close to that of the positive exclamative:
How tired my arms are!
The understood meaning is that the speaker's arms are very tired.