The experience bomb is being explained as the result of learning something particulary useful in a fight, e.g. a new trick which you hadn't thought of before.

Could someone elaborate on what these useful tricks are? Do you just need to kill something in a different way than you had been or do you need to do something specific? If it's specific what needs to be done?

No, I don't know. Maybe it's incorporated into the game mechanics like an extraordinary dice roll : Hitting the 1 three times means something extraordinary -> experience bomb.

It's just a suggestion, merely speculation, nothing else. We've never been told how it actually works, except this archived discussion.

When you find a big kettle of crazy, it's best not to stir it.
--Dilbert cartoon

"Interplay.some zombiefied unlife thing going on there" - skavenhorde at RPGWatch