At the luncheon in Fitzgerald's The Great Gatsby, how is Daisy acting toward Gatsby? What does Tom say to Nick about this?

At the luncheon, Daisy is acting very flirtatiously toward Gatsby. She says things like, "You always look so cool," and "You resemble the advertisement of a man." These seemingly innocent comments are actually deeply representative of the situation that Daisy finds herself in. In terms of setting, the drawing room in which the luncheon is held is stifling. The "day was broiling, almost the last, certainly the warmest, of the summer." Upon Nick's entrance, the women, Daisy and Jordan, both assert, "We can't move." In this instance, Fitzgerald is representing the intensity of the situation with the heat that is literally and figuratively suffocating. This "heat" is the anger of Tom Buchanan, Daisy's husband who discovers Daisy and Gatsby's affair when Daisy mouths to Gatsby that she loves him. "It's so hot," Daisy insists, on the verge of tears. Clearly, Daisy is unable to cope with the pressure exerted by her husband, and the "cool" Gatsby represents an escape from the heat that surrounds her. 

After seeing Daisy mouth to Gatsby that she loves him, Tom suggests that they all go for a drive into the city. On the way, he asks Nick, "Did you see that," referring to Daisy telling Gatsby that she loves him. After Nick feigns ignorance, Tom realizes correctly that Nick and Jordan must have known all along about the affair. Tom then asks, "You must think I'm pretty dumb, don't you," and goes on to reveal that he has made an "investigation" of Gatsby's past. This passage is important because it is later revealed that Gatsby is involved in the criminal underground, and Tom eventually uses this information to convince Daisy to leave Gatsby.