I've never been able to do this before, but now I know somebody who is having twins (in the next month) and they don't want to know the sex of the babies. So I'm gonna guess what they'll be. I've got a 1 in 3 chance right?
My guess is two boys.
Though the mom was kind of hoping for a boy and a girl. Hmm... I'll probably be totally wrong, but it's fun to speculate.