Unexpectedly, explosions start to go off in the mines while Basilio and his brother are talking about school. They count the explosions and escape the mines before anything can happen. Not violent, but certainly intense as the kids are genuinely frightened.
The image of Tito, the devil, can be scary to some. The devil in the parade scene towards the end may be, too.
The documentary as a whole is very dark and hard to watch because of its subject matter--miners, including children, see no way to ensure their protection except to beg mercy from the Devil with sacrifices.