Anomalous angry face behavior

Whenever the player in Doom holds down the "fire" button for a prolonged period of time, the status bar face can be seen gritting its teeth angrily. However, in certain circumstances, it is possible to activate the "angry face" without holding down the fire button, or even without firing a weapon at all.

There are a number of ways to see this effect:
 * Pause the game or activate the menu while the player's weapon is in the middle of a firing or reloading animation.
 * Start a new game, then immediately activate the menu or pause the game before the player's pistol is fully raised.
 * Start a new game, then immediately switch to the fist, then keep repeatedly and rapidly switching between the fist and the pistol.