The Giant jumps up and down vigorously on top of the enemy. Before it starts, the Giant must test to determine if it. If it falls over, work out where it falls and calculate damage as already described. Any wounds caused by the fall (on either side) count towards the combat result. If the Giant remains on its none-too-nimble feet, it will inflict two attacks.
Giants enjoy jumping up and down on their enemies so much that a Giant that does so in one combat round will automatically do so in the following round if it is able to, assuming that it did not fall over in the previous round. A Giant that starts to Jump Up and Down will therefore continue to do so on the same target until it falls over, the target is destroyed, or the combat ends.