Revealing mistake: After Dante's Peak explodes for the final time, the pyroclastic cloud rolls down the mountain toward the town. Harry shouts "Don't look back, kids, don't look back." and then we are shown a wide shot of the truck zooming down the ash-choked streets. Unfortunately, it's painfully obvious that this is either a miniature or CGI shot, because the truck isn't leaving any tracks behind it or trailing any clouds of ash despite its high speed. (01:28:19)
Revealing mistake: In the scene where the van is about to be flipped over on the washed out bridge, wires can be seen on the hood of the miniature that pulled it across.
Revealing mistake: When the volcano begins to erupt, cars are seen driving out of the city. When the motorway collapses, and the cars go with it, in the close up shots, there are no drivers inside them.
Revealing mistake: During the pyroclastic flow scene, the flow sweeps a tractor trailer off an overpass, which blows off some of the side panels in the back. Watch the back of the truck before the flow hits it, the panels that come out are already popped out and ready to blow off.
Revealing mistake: When the group is first leaving shore in the boat in the acid lake with the cabin behind them on fire, the angle of the river behind them compared to the shore line doesn't match and moves independently showing how they matted the two different scenes together.
Revealing mistake: When the lava comes through Ruth's house you can see that it's done with CG. The reddish "streaks" look like from a sci-fi movie. The shapes of the lights and streaks are unnatural.
Revealing mistake: While the scientists are trying to escape, Paul and his truck get tossed aside into the swollen river, but the truck is suddenly much smaller than it should be.
Revealing mistake: When Lauren screams after seeing the bodies in the hot spring, someone grabs her, but it is none of the characters in the scene.
Answer: He's young and he and his sister are alone. He's worried about his Grandma and she's not answering the phone. He's saying hello because he desperately wants her to answer so he knows she's OK. He feels helpless just letting the phone ring.
The_Iceman