What the First Gravedigger meant to say was se defendendo, Latin for self-defense, which was (and still is) used as a legal term. He humorously picked up on his colleague’s use of “so” in the previous line and invented a phrase which sounds like self-offense instead of self-defense. Toward the end of this speech he botches another Latin word when he uses the non-word “argal” for the Latin ergo (therefore).