I once observed a deaf dog owner fingerspell manually T-R-Y to her dog at the right eye level when it refused to climb up the steps of a stair too steep for the dog to climb. The dog obliged. It looked to me like the master fingerspelled the word spontaneously for the first time, not a rehearsed command, like roll-over, sit-up, etc. We know dogs do follow a limited number of signed commands. But to follow to a fingerspelled command is unheard of. It is exactly equivalent to tasking it to read a written word.