So sometimes that's correct - for instance, it is almost always humid and darker beneath the trees. And there are definitely insects! What I wasn't picturing - and what is, it turns out, an integral part of this particular rainforest - was the bamboo.
The forest here is situated on a floodplain, which means that it undergoes natural disturbance pretty frequently - the river will overflow its banks, or meander into a different direction. Sometimes a big tree falls over and brings down all the other trees in its path. When this happens, the first thing to grow up is bamboo. So a lot of the time, what the monkeys are doing is jumping from isolated tree to isolated tree in a sea of bamboo. And what this means for those of us following said monkeys is swimming through this sea of bamboo in vain attempts to make it to those isolated trees before the monkeys have headed to another one!
I can see what you're thinking. "Bamboo? What's wrong with bamboo?" Well, I've learned that bamboo has a number of really terrible qualities. It doesn't have the tree cover that the rest of the forest does, which really does make a substantial difference in temperature. It's also frequently a haven for fire and bullet ants. The big bamboo stands are usually considerably taller than I am and don't really want to be pushed through - fortunately, we've developed a specific technique for fighting our way through. Our Bamboo Tramping Technique involves me lifting my forearms in front of my face and basically falling forward. By continuously falling forward, you flatten enough bamboo out to create a path. It can be pretty resilient, so you have to work up a good head of steam before you can move through with any speed (and it also likes to spring back up behind you). We've been going at the same general routes for long enough that there's a really respectable trail out there in the middle of the bamboo that the monkeys traverse most frequently, but on those occasions that the monkeys change it up, it's time to tramp through more bamboo!
The other exciting discovery I've made about bamboo is that it frequently has thorns. Big, thick thorns. Sometimes, when the thorns grow long enough, they form thorn-branches which in turn grow thorns! The thorns on thorns are still sharp and uncomfortable. They're really good at catching on shirts, or bandanas, or hair, or hands.
However, the upshot of all of this is that I have gained a newfound respect for Panda Bears. And for that, I am greatful?