How do I casually follow-up with a POI?

[livincoastal]

So I've found myself in this situation a few times.  I have sent initial emails to POIs expressing interest in studying/working with them and their program.  They send me a response that seems promising and begins to open up dialogue, maybe even asking a question or two.  I then reply to this message aaaaaand then there's some dead air.  My question is how do I casually, subtly send an email to kind of push them to respond to my previous message without coming across as pushy or impatient?  And also how long should I wait until I send such an email?  The POIs seem very interested in pursuing conversations and discussing research, and I am super motivated to keep the dialogue going but I want to avoid "bugging" them or coming off as overbearing or annoying.  Any tips would be appreciated!!

[TheGirlWhoLived]

Whatever you do, I would wait at least week before saying anything.