Humidity curls our hair and dots our brow with sweat. And there are only a few reasons worth enduring it: tiny howler monkeys with tiny hands and tiny ears; sleek, whiskered river otters; three-toed sloths and stoney, ancient-looking manatees. These and hundreds of other creatures inhabit the Orinoco--Secrets of the River rain forest exhibit at the Dallas World Aquarium, which re-creates a section of Venezuela's Orinoco River basin. There's more to this aquarium than fish, which, in our opinion, are nothing in comparison with the seven-level rain forest. Sorry, white-spotted bamboo shark and stingray. There are also penguins, but they're South African penguins, so look for them outside...where it's almost as humid and muggy.