A wh-expression without wh-movement, where the wh-word is the object of the preposition “about”:
You are talking about what?
A sentence that has undergone wh-movement:
What are you talking about?
⸺with a pied-piped “about”:
About what are you talking?
A question — This doesn’t seem acceptable; why can’t the “talking” get pied-piped as well? Or, can it?
Talking about what are you?
Similarly (I find),
A wh-expression without wh-movement, where the wh-word is the object of the preposition “of”:
Chills and headache are symptoms of what?
That above, with wh-movement applied:
What are chills and headache symptoms of?
⸺with a pied-piped “of”. A question — Is this structure acceptable? Why, or why not?
Of what are chills and headache symptoms?
The entire wh-clause has gotten pied-piped:
Symptoms of what are chills and headache?
Why can’t “-ing about” get pied-piped in wh-movement when “(noun) of” can be? What exactly determines what can be pied-piped and what cannot in wh-movement?