Trigger bounce, is induced generally mechanicly...by having too fine a trigger pull...as the gun fires, it moves...and your finger against the trigger, fires the gun again...that way, its possible for the gun to keep firing as if it was Full Auto...in really sensitive casses....the gun can fire without having your finger near the trigger...and goes runaway.
Particularily prevalent in E1 Cockers..due to the large moving mass, of bolt, back block, pump arm etc...this is why the E2 was developed with software, to remove bounce.