Three of my guys come out when I slap the ground at the entrance to their burrows.....or if they feel me walking around messing around outside/inside their enclosures my old man humphry gets his foot tickled..and he spins around and comes on out (as he had a cinder block hide and not a burrow for me to knock at....
You will want to have a REALLY YUMMY treat the first week you are forming this communication with them