Why do girls do this?

[coldmarch]

You're not the first one I see having this issue: some girls poke you and then expect you to put contents in the conversation or ask questions. They would rather stay completely silent instead of carrying the conversation themselves, if you aren't reacting.
Some guys see it as a chance they give them to conquest them, while others are just pissed and dismissive about that (as I would be as well, to be honest).

However, this reveals some possible scenarios about the girl:
1) She is extremely shy and doesn't even dare about initiating anything which exposes her personality.
2) She is indeed as empty as it seems.
3) She is very selfish and wants to be covered of attentions without moving a finger and without even asking things about the guy because she isn't interested in him as person but only as attentions-service.
Probably the best case is the 1, but I think you should first of all understand what you want in a girl and what she is suggesting to be might not match your requirements, that's maybe why you're bothered. Either way it suggests to be a bad balance between cost/quality for now, because the dynamic demands things to you but then gives nothing back. Well, for now. You can still give her more time and discover if she was just extremely shy (hiding worthy contents and interest in you) or not really a big deal.

[Anonymous]

I don't know but that's a good question. My bottom left leg hurts, can you rub it?

[WesBrewer]

Sometimes it is hard for them to think of anything as well, I have the same issue with some friends I have.