The set-up is similar to the baseball skit with a horizontal poncho screen, except this time it's backlight with a Coleman lantern about ten feet behind it, so everything in front of the lantern and behind the poncho is silhouetted.
The "patient" is brought in and made to lie down behind the poncho. He is then opened with a bow saw (with suitable kicks of his feet) and objects (mess kits, canteens, etc) are "removed" from "inside" his body. All of this actually happens behind the patient (closer to the lamp), but the screen makes it look one dimensional.
For a finale, the patients head can be removed with an axe and he can get up and walk around the front of the screen with an oversized shirt buttoned above his head.