Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
Tarzan is leading Jane, a group of whites, and some Africans through a steaming swamp that is full of man-eating Iguanas. (Yes, seriously - some are Green Iguanas, others are another type of Iguana I'm not sure about.) One of the Africans falls in and we see several lizards running towards the water and diving in. Then we see the man's hands held up out of the water slowly disappear and by the look on Jane's face, we know that the iguanas have torn his flesh to shreds and feasted on his corpse turning the water red with his blood. The movie doesn't show any of that, of course, but that's the way I imagined it - a herd of pet store lizards on the wrong continent ditching their vegetarian diets and dining on human flesh. (I'd watch that movie.) Jane almost falls in herself, and some iguanas come running up to grab her but some guy saves her. That part was just to give us another look at Jane's bare thighs - pretty racy for 1936. Then the nasty guy who stuck Tarzan in a cage to ship him home as a sideshow freak wades into the water to grab a big stick to fight Tarzan with but he falls into some quicksand and he also becomes Iguana chow.