So this lot I have always has an issue with weeds; the lot literally gets full of them after only a few Sim hours, even if my Sims and the (dreaded) butler pull the weeds out.
So my Sims are both elders; two of their twin daughters just graduated college (one being a part of the Tri-Var Greek house) and the other is currently a Semester 1 senior. Anyway, the male Sim is/was named Myles, and I was thinking, "Maybe I should see if he'll die by satellite if I make him stargaze/watch the clouds." (It was nighttime.) So I sent him to just pull some weeds first, and the moment he touched the weeds, he went up in flames! It wasn't caused by lightning, either. Can weeds... ya know... catch fire? (He's sort of dead now...)

Was it summer? I've had visiting Sims spontaneously combust after spending too long in the hot tub in summer (they love that hot tub) before I got a mod that prevented temperature extremes. I suppose physical activity like pulling weeds could also cause that.

Yes, it was summer, but he wasn't in the hot tub. Wouldn't he have passed out due to heat stroke, though?

Sims don't always pass out from heatstroke. Occasionally, they'll just combust instead. Spending an excessive amount of time outside in summer, doing physical activities like jogging or gardening can lead them to overheat and combust.

The hot tub was just an example : ) The hot tub, baths, showers, physical intimacy with other Sims, and exercise all increase your Sim's temperature. I can't recall if pulling weeds gains body skill/counts as exercise, though. Not sure about the heat stroke. Spontaneous combustion just seems to happen... spontaneously. I guess there's a random chance of it happening.

O_O
Okay, I'm getting rid of Summer in Pleasantview.

You can also download that temperature mod. My Sims haven't combusted ..... yet ... and I downloaded the mod a few years ago. I thought I saw a couple of these mods (maybe not), but the one I downloaded was Carrigon's from the Sims 2 Workshop. My Sims sometimes need to be teleported inside because they will just stand there and freeze or overheat now, but at least they won't die.

Do realize, though, that this might affect sunburns and social workers.