What is the boss like? Why doesn't Lennie answer him? How does the boss feel about Lennie's mental slowness

The boss wastes no time with small talk and gets straight to the point.... namely addressing George and Lennie's ability to work and collecting their work slips. The boss is put off by Lennie's silence, but all the more annoyed by George answering for him. Lennie's mental slowness isn't an issue, as long as Lennie can perform his job. The boss' one point of contention is George's motive in traveling with Lennie, and he infers that George might possibly be collecting Lennie's paycheck. George counters this by telling the boss that Lennie is his cousin, and he promised his aunt he'd look after him.