Ah, well let me try it again but with a more specific thought process. The dildos would have 2 or 4 chambers filled with either a liquid chemical or a solid chemical suspended in a neutral substrate that would discharge out a mixing nozzle in the head of the dildo when it reached a specific surface temperature. Either from friction or prolonged contact with aroused flesh. The Chemicals themselves would probably be sodium and something that reacts rather violently with it like water or something that releases hydronium ions in solution. Suitably explosive to burst an unfortunate belly (or chest if shoved down a gullet) but not so much it'd carry any force beyond the original squishy sack it finds it's self in. Well, probably not; I don't recommend anyone have volatile chemicals reacting super close to them. They might get hit by shards of who knows what!

For the scenario specifically ideally you'd want a close knit group of girls that share a bond but also exist in a strict hierarchy. The kind that breeds resentment and bullying; perhaps a schoolbus of giddy little cheerleaders? Moving onto the actual game the dildos would have to be placed on and in the girls with a locked belt; closing off the obvious point of entry for the other dildos and forcing any girl on girl violence to be exclusively oral or anal in nature. From there it really depends on the personality of the girls in the scenario doesn't it? Would they form into groups to try and hunt eachother only to be back-stabbed in the anus? Or would it devolve into a free-for-all where every girl is out for herself the rest be dammed? And what if some of them are willing to sacrifice themselves for another girl they secretly (or openly) love in the group?

>Which one? The chemically inflating one?

Yes, that one. You'd need a test subject to try it out before making enough for a whole mess of girls after all. Imagine if it didn't work and Bob wasted all that time and effort! Or worse, imagine if it did work but not nearly well enough and instead of popping a girl open it just killed her! Madness!