Something like a marionette's string. This will require careful centreing and balance, and care on the part of the owner of the palm not to force the masked actor to overreach and fall over. During other sessions I offer each student a hand puppet. Then in pairs I get them to sit facing one another and improvise a scene between the two puppets. Only after they have mastered the combination of movement and voice do I get each pair to go behind the booth and do a scene with the puppets performing on a playboard.
Many students take some time to understand the projection needed.
Currently I am experimenting with movement awareness regimes such as Feldenkrais and Tai Chi Chuan in order to promote the somatic control demanded by mask work. I find standard mime exercises although a handy adjunct can be limited by their ready subtlety. Masks and puppets demand large gestures at varying paces. They're always very open and never complex but exact and purposeful. Japanese Noh drama is the essence of that steady state performance.