What were the gusrds doing that kept them from beating the prisoners?

From the text:

"On the way, we saw some young German girls. The guards began to tease them. The girls giggled. They allowed themselves to be kissed and tickled, bursting with laughter. They were all laughing, joking, and passing love notes to one another. At least, during all that time, we endured neither shouting nor blows."