Why is the boss suspicious when he meets George and Lennie?

He believes Lenny is slow, but George assures him that he might not be bright, but that he's a great worker and strong as a bull. The boss thought George was taking Lennie's pay as well. Men do not usually travel together.

The boss does not understand the reason why George answers all the questions and not letting Lennie talk. first he thought that Lennie was shy and playfully asked "he ain't much of a talker, is he?" This foreshadows that even though he thinks Lennie doesn't talk much there is something behind his story.

however, when George answer the boss "Oh! I ain't saying he's bright. He ain't. But I say he's a god damn good worker". (He is trying to hide the boss about Lennie's personality. Because he does't want the boss to know how stupid Lennie is.) But the boss raised his voice and talked seriously,"say-what you sellin" and "you takin' his pay away from him?"

Although, George tries to delay everything and tell the truth without really revealing everything, still the boss are not satisfied by his excuses.

The idea, the fact that the two men are travelling together, just can't go through the boss mind. Because he is not used to and does not want to believe it now, either.He rather has his eyes on them.