In Chapter 3 of Night, what was Bela Katz forced to do once he was chosen for his strength?

Because of his great strength, Bela Katz was forced to be a part of the Sonder-Kommando, the Jewish unit that worked in the crematories.  One of his first jobs had been to put his own father's body into the crematory oven.

In Chapter 3, Elie and his father have just survived the selections upon arriving at Birkenau.  For the present, they are alive, but as some SS officers move around their barracks looking for "strong men", they debate within their own minds the best means of ensuring their further survival.  Elie wonders if, since the officers are so interested in strong individuals, it might be best to "pass oneself off as sturdy", but his father does not agree.  Elie's father believes that above all, it is better not to draw atention to oneself. 

Later on, Elie learns that his father's inclination was correct.  Bela Katz, the son of a tradesman from Sighet, had arrived at the camp a week previously, on the first transport.  His strength had been quickly noticed, and he had been forced into the most odious of jobs, carrying the dead into the crematories.