You should just wait until the shroom starts to move on the rock. The way actinoduscus mushrooms reproduce is they leave a piece of foot as the mushroom moves around. so i wait until the shroom has moved a little. it will look like its nudging the foot out on one side so you take your blade and slice the nudging part to separate it from the mother. once its seperated the piece of foot will grow into a baby shroom. Thats how i "force" the shroom to reproduce. remember, the side that gets sliced will take on more of the coloration of the mother on that side of the shroom you cut.