Why do you think Crooks frightens Lennie with the prospect of George not returning from town? Why does Crooks regret doing this?

Crooks feels isolated and subjugated on this ranch. The chance to have power over someone else is too enticing to pass up. Crooks knows he can scare Lennie and perhaps, for a few moments, not feel so weak and vulnerable. Unfortunately, Lennie's confusion turns into anger and Crooks needs to backtrack and apologize.