Complex sentence: On the way back, Nauls cuts MacReady loose from the tow line, assuming that MacReady has been assimilated when he finds a torn shirt with MacReady's name on it.
Split into simpler sentences: On the way back, Nauls cuts MacReady loose from the tow line. He assumes that MacReady has been assimilated when he finds a torn shirt with MacReady's name on it.