If you get too close to a wild one that used it's special ability (a charge that will set it on fire and aggravate nearby dinos) it'll display a message saying "getting hot! Stay away!!!!" and that will set you on fire. Don't approach unless you know you're prepared.
Be careful with traps in Lava biome, if a Magmasaur Argos to your structure, it can blast a huge hole in your stone easily. One got trapped in our pitfall trap and we became aware of it from the tribe log showing it had destroyed half the building in minutes. This was NOT a small structure either. Best to break it out and kite it away (or eat it with Rexes). Stone, metal and Tek are all damaged or destroyed by this thing. It was not designed to be trapped or to be held in structures. If you want to tame one, steal an egg.