Two units, next to each other, both with Walking Bomb. Unit A is weakened to near death. Unit B is then killed. The Walking Bomb from unit B kills unit A.

In this situation, the walking bombs will cycle through, killing each other many times. When the fight is over, the combat recap will badly miscalculate how many enemies were actually killed, and assign exp which can be easily in the tens of thousands, if the mutually destroying units were fairly high-level and worth a lot. This only works if the walking bombs chain off each other.