Arms Don't Work That Way

(Context: playing a star wars rpg session during old republic times; our Wookie DJ, Dewkaza, goes up to a Mandalorian to kill him)

Dewkaza: I grapple the mandalorian in front of me

Dewkaza *rolls* : Natural 20! I pull his arms off!

GM: Alright, roll strength

Dewkaza *rolls* : Uhh. 4

GM: The mandalorian starts screaming and crying 

Dewkaza *rolls*: I try again! ….. 4 again

GM: The mandalorian continues screaming and crying as you keep trying and failing to pull his arms off

Me: *makes mock crying and wailing noises*

Droid: Oh my God, I go over and stab him to put him out of his missery!

GM: Ok, the mandalorian is stabbed and STILL alive and is still crying in pain —-all other enemies are defeated; mandalorian is still grappled——

Jedi1: Jeezus, ok I go over and execute him with my lightsaber *rolls* 8

GM: You miss.

Dewkazza: Wait wait one more time! *rolls 14* 

GM: You finally rip his arms off and kill him.