Horton's climb
Under the Kwuggerbug's command, Horton is forced to climb up a mountain to get the Kwuggerbug. Seuss uses imagery to describe how much Horton is suffering during the ascent, saying that: "he dragged his tired legs over rocks and big boulders. He stumbled and staggered uphill, over stones that tattered his toenails and bruised all his bones." Overall, we see how unfairly Horton is being treated, and how cruel the Kwuggerbug is.
The Beezlenuts
The Beezlenuts are described with imagery in order to show how delicious and desirable they are to the animals in the jungle. For example, the narrator describes them as being luscious and sweet: "and he picked all those nuts and he stacked a big mound of luscious, sweet Beezlenuts high on the ground."
The crocodiles
The crocodiles are described using imagery in order to show how dangerous and frightening they are. For example, Horton describes their "terrible teeth," and how they "flash." This imagery is used to emphasize how difficult crossing the lake will be for Horton, and how much danger he is putting himself in for the benefit of the Kwuggerbug.