In 1973, an artist named Michael Craig-Martin put a glass of water on a glass bathroom shelf and insisted it was an oak tree. In 2006, the playwright and actor Tim Crouch responded to Craig-Martin by conducting a psychological experiment and calling it a play.

It is a work for one performer and one victim: The performer is Dennis Kelly, who plays a hypnotist—not a therapist but a comedian, of the "cluck like a chicken" sort who appear at every county fair. He is running through his act at a local bar, but admits he's only doing so to honor old bookings, because for the past three months his mesmeric chops have failed him. For the past three months he's been unable to concentrate, because three months ago he struck a 12-year-old girl with his car, killing her. 

The victim, who is played by a different actor each night of the run, is the girl's distraught father.

The actors do not know this. Indeed, for the piece to work as Crouch intended, they must know nothing whatsoever about the performance. Each night, the actor playing the father enters the theater with the rest of the audience, takes the stage when the hypnotist asks, and does whatever he tells him (or her) to do. Sometimes the hypnotist whispers directions to the actor directly; sometimes he asks him to read dialogue from a clipboard; sometimes he turns his face to the back wall of the theater and murmurs instructions over a wireless headset; on occasion he just interrupts his patter with a command. 

The hypnotist does not realize, at first, that his volunteer is the father of the girl. As the situation slowly dawns on him, the distinctions between what is stage direction and what is hypnotic command grow fuzzy. At one point, he breaks to ask the actor playing the father what he thinks of the whole endeavor, but the answers are scripted. Ultimately, An Oak Tree is not about a dead girl but about power dynamics and control. I assume that the performance you see will not be the one I saw (with Matthew Kern, who was very game, as the father), but it will definitely be a strange and maybe mesmeric experience.

SEE IT: Lincoln Hall, Portland State University, 1620 SW Park Ave., 8 pm Wednesdays-Saturdays, 2 pm Sundays. Closes July 31. $10 suggested donation. All ages.