Moreau has a bloody rag in his left hand, and the scalpel in his right.  When Prendick opens the door, he does a Left-Right swipe with the rag and then stabs the scalpel straight at Prendick (but not so much 'attacking' as 'wildly gesticulating'), who avoids back and then jumps back.  Moreau  follows up on this, and Monty interposes himself.  Moreau returns to the Operating Theatre.  When Monty re-enters, he gets between Prendick and the exit, whereupon Prendick rips a piece off the set (railing of the staircase?) and slashes U-D (M jumps back), UL-DR (M avoids R), and then smashes M in the head with an U-D hit (active knap), before running off.