Steinbeck creates tension in this scene in two ways. The first is Curley’s body language to suggest to the reader that he is on the defensive. For example, when he first sees George and Lennie, he looks at them coldly. The use of the word coldly suggests unfriendliness. Next, his arms bend at the elbow and he clenches his fists. This stance suggests a person ready to fight, even though George and Lennie have done nothing to him. Next, “he stiffened and went into a slight crouch.” Again, this suggests someone who is ready to fight, or what we might call “spoiling for a fight.” His glance is calculating and pugnacious, so he is both sizing the men up and challenging them. This makes Lennie nervous, and he shifts from foot to foot. This all leaves the reader wondering what is going to happen next.
Another way Steinbeck creates tension is the way Curley speaks to George and Lennie. When he asks Lennie a question and George answers, he “lashes” around and says, “"By Christ, he's gotta talk when he's spoke to. What the hell are you gettin' into it for?" The combination of his whip-like movement and the way he speaks to George makes Lennie uncomfortable, but more than that, it lets the reader know that Curley likes to confront people, and that he probably will confront George and Lennie again.