So has anybody ever shot a ghoul, and immediately following it combusted and bursts into flame? This has happened to both me and my uncle on separate occasions. And I was curious if this has happened to anyone else, or if Bethesda can confirm or deny this.

What weapon were you using? Can't some vaporise on critical hits?

Laser weapons can turn targets into a pile of smoldering ash. Plasma weapons can turn targets into plies of green goo. As far as them "combusted and bursts into flame" your muzzle flash could have been in a gas pocket and I believe with laser weapons if the beam goes through a gas pocket that will also light the gas.

Correction. Laser cuts people in half, pulse turns people to ash, plasma turns stuff to goo and fire torches people

Lasers turn people into ash as well.

In F3 yes but not in F1 & 2. At least I can't remember it happening

As far as i know you're right.

That's in previous Fallout games, in Fallout 3, laser weapons do indeed turn people into ash (though I have also seen them take limbs off.) I think the cutting people in half thing makes more sense, given that a laser is a focused beam and should therefore cut through a small area rather than turn the target into a pile of ash, but nonetheless in Fallout 3, which must be what this topic is about, given the mention of VATS, that is indeed what it does.

Anyway, the "Bursting into flame thing sounds like it could be caused by a gas leak, sometimes you will find them in Fallout 3 around pipes, they can be identified by distortions in the air, and can be ignited, most likely, you ignited one while attacking this ghoul.

We all have to remember how random and cool the people were that made the first Fallouts. There is so many little gags and hidden things everywhere. Gouls are radioactive right? Mabye there is is like some kind of 0.005 chance of all gouls combusting. It seems like something They'd do. If UFO's and T-Rex foot prints why not sponateously combusting gouls?

Thers a special version of the chinese pistol which fires incendary rounds you can find, were you useing that? Theirs a building I know of where there are ferol ghouls and supermutants, and after you kill them there head explodes whilst their laying on the floor, which is nice.

Theres also gas in the tunnels that some weapons (like lasers) can sometimes set alight.