What is sadism and where do you see evidence of it in Night by Elie Wiesell?

Sadism is extreme cruelty, and it is seen throughout Elie Wiesel's book Night. When Moshe the Beadle returned to Sighet after having been taken by the Nazis, he told the villagers how he and the others were forced to dig their own graves and then were shot. That's sadism.

The Nazis treated the Jews as though they were vermin, and many Nazis enjoyed employing cruelty. When Elie and his father were being marched toward the fire pits at Birkenau, and Elie saw a truckload of babies and children thrown into the pits, that was sadism. What decent person does something so horribly cruel? Prisoners were beaten, starved, hanged, shot, tortured in different ways in the book, and the Nazis took a perverse pleasure in this. One of the worst instances of sadism was when the Jewish prisoners were forced to watch a young boy hanged--a boy who because of his low weight did not die right away and was left swinging by his neck until he did. The Nazis were the kings of sadism.