Macomber's sick stomach is echoed in the sickness of the lion – both of them are prey here. Macomber and the lion both end up on the wrong end of a gun. In the "Symbols" section, we have discussed the connections between Macomber and the animals he seeks. So here we'll just remind you that these animals highlight Macomber's own vulnerability. His life is in more danger than he realizes.
Where Wilson is strong and virile, Macomber is weak and fumbling. Every time Wilson's hardiness shines, Macomber looks all the more like, well, a doofus. This is never more clear than when Margot's attentions turn from disparaging her hapless husband to admiring the handsome hunter.