User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-9031680-20130925073119/@comment-4009941-20130925075904

The explosive Brachydios uses a Slime Mold http://en.wikipedia.org/wiki/Slime_mold that forms a special bond with them, its horn holds a supply of it like a bucket if you noticed also this unusual Slime Mold is explosive and can be activated (Turns green when ready to spread spores) by Brachydios from something in its saliva and horn.

So its not just a matter of heat alone its a matter of living things being activated into spreading spores but in the process cause explosions that Brachydios uses in his side of the bond.

As it explodes spores go into the air and when they land on a Brachydios they grow into the Slime Mold you see them all use.

Note Slime Mold is able to actually travel across land instead of being stuck in place like plants making it very unusual to alot of people.