It's not us interacting with them. Telling them what to do or anything like that. It's them interacting with us. Acting something out. What each girl is acting out varies a bit.
The interactive cards have short clips called "_it" clips. VirtuaGirl cards currently seem to have more "_it" clips than DeskBabes cards have though.
The best way I've found to view them, for me, is to activate just one card, set it to small size and just let it play on it's own. You'll see the short interactive clips.
I see them more often between clips that have "magic at start" and/or "magic at end". Can't say if it's like that for everyone.