This is a progressive drill:

First have 3 defensive linemen at a time lineup and face the coach, who will do the head motions. The defensive line man must react quickly to the head movements.

Next pair up the defensive linemen, and a coach standing behind the designated defensive lineman signaling the kind of block and snap count to the designated offensive lineman. Have the defensive lineman react to the movement of the opposing offensive lineman.

Finally, lineup one defensive lineman against three offensive linemen to work on correct reactions to away and combination blocks. Again the coach will stand behind the defensive lineman and signal block and snap count.