The Pantanal is a truly amazing place for wildlife. It should come with a health warning for biologists (or any wildlife enthusiast): "WARNING: liable to cause heart palpitations and shortness of breath". Here are a few of my favourite wildlife encounters, and there are more photographs on my Brazil flickr set.
Troupials are the most orange bird I've ever seen. Their plumage is made up of highly contrasting patterns of black and the shade of orange usually seen on fluorescent safety jackets. The first time one swoops in front of your binoculars, you nearly fall over with the impact of the sensory overload. They also have a very distinctive and easy-to-imitate two-note whistle, so you can have fun whistling like a troupial and hearing them respond. This probably annoys the hell out of them, as they look around fruitlessly for the phantom troupial that they can hear calling. But if you can't mess with the mind of a troupial every once in a while, what fun is life?
I saw a little agouti (possibly the same one) several times. They are quite shy, but if you sit quietly for a while in the right place, eventually one wanders past. They make a noise out of all proportion to their size, and when you hear one coming through the undergrowth it sounds like a small tank. If you're quiet (as I was), you can get a good look at them before they spot you and barrel off into the forest at a furious pace.
Black howler monkeys
I made a recording of the howl on my camera, so you can hear it for yourself. I'm afraid it's a WAV file, but Quicktime plays it without any problems. I promise that there's no electronic trickery in the recording. The real thing sounds just like that, but much louder.
One morning I was showering and noticed a buff coloured lump on a the branch of a tree through the screen window. I wondered idly if it was a female howler monkey or an owl or similar bird that I hadn't seen yet. When it reached out an arm for a leaf, I saw it was a monkey and caught myself thinking, "Oh, it's just a monkey". Then I did a bit of a mental double take. Just a monkey. Through the bathroom window. The Pantanal does that to you after a while. You become blithely casual about the most amazing of wildlife sights: 100 caiman? Yawn. Darling, I don't get out of bed for less than a giant anteater and a jaguar a day.