when you select a weapon, your worm plays an animation of drawing it, unless his state does not allow using a weapon
a worm also draws his weapon when recovering from such state
different weapons are used differently and have different modes and states, like homing missile having "set target" and "fire" modes
and interruption is when you are knocked or hurt when your attack is in progress, the weapon will fire a random shot and the attack is cancelled
and also there probably will be an animation after attack when worm removes a weapon