The Doctor and Osgood in “The Zygon Invasion”

[points to the question marks on Osgood's lapel] Oh, I see you've accessorized it.

Yes.

The old question marks.

You used to wear question marks.

Oh, I know, yes, I did.

They were nice. Why don't you wear them anymore?

Oh, I do. I've got question mark underpants.

Makes one wonder what the question is.