I think Curley was taking in his next opponent and gathering things that might give him an
advantage if they did fight. Curley is a guy that picks fights against people that are larger than him and if he loses he blames it on his opponent's height. Curley is a wannabe tough guy because he just wants to prove how manly he is by fighting and it massively backfired when he tried to beat up Lennie. I think in the text when it said measured his reach it's a big indication that he wants to fight George and dodge his punches. Curley looks at every man like an opponent so him taking in some attributes of George is probably very common for him and Curley wants to be the most dominant man all the time.