How do I kill a process that won't die?

I'm unable to kill a process using any of the techniques I'm aware of ("Force Quit" in Activity Monitor, top, killall from the Terminal) and wonder if there are some additional steps I can take. ~ $ sudo killall -KILL 77439 Password: No matching processes were found ~ $ killall -KILL 77439 No matching processes belonging to you were found ~ $ killall 77439 No matching processes belonging to you were found ~ $ killall Mathematica No matching processes belonging to you were found FWIW the process is "Mathematica" which I cannot relaunch, Quit, or Force Quit, or sample, either by name or PID, and it appears to have some odd side effects (screenshots don't appear, can't empty trash, and can't even shut down the system). Are there additional steps that can be taken to really *really* kill a badly behaved process?