Scream 3 - If Only They Knew What They Put in the Script!
When we find out who the killer is, and Sidney disappears we see her behind the bar. She takes an ice pick out of the bucket and stabs Roman with it. He falls on the ground and he lets the knife out of his hand. She takes the knife and stabs him with it. Whoops! It is actually the ice pick sticking out of his body!
At no point does Sidney stab Roman with the knife. After Roman drops the knife out of his hands. Sidney picks up the knife and tosses it aside - out of Romans reach. If you have a wide screen copy of the movie, play it on a big screen and you'll see. She actually stabs him with the ice pick. You're slip-up is wrong.