The most weasel
Giant otters (Pteronura brasiliensis)! They get up to 6 feet long and can weigh up to 80 pounds. (To put this in some perspective, that’s about the size of a female sea lion.) They’ll work with the unbelievably horrible river dolphins to outwit fish and the occasional human, they live in packs and defend territory, and they always look unhappy when they’re eating.
Or rather they tend to look pretty pissed off in general, and they don’t stop even when they’ve got food in their faces. I mean, they’re mustelids (ferrets, weasels, stoats, etc.), so you’d expect more of a playful or self-satisfied look to them, but nope. Angry and bitter.
Above: Fuck you and the canoe you paddled in on, buddy.
Those cream patches on their throats are consistent across their lifetimes and are distinctive enough to allow the identification of individuals based on neck patterns, which is very handy for researchers.
The otters themselves tend to communicate much more with vocalizations, and they’re one of the talkiest of the otter species, most likely because they’re also one of the more social ones. Their family packs can have over a dozen members and consist of a breeding pair, older offspring, and the current crop of 1-4 cubs, with everyone pitching in to care for the babies.
There’s a positive pressure favoring larger groups where possible. More cubs survive to adulthood in larger groups, and they’ll readily team up to take down prey they can’t handle one-on-one (usually smaller anacondas and caimans and larger fish), pointlessly and dickishly harass large predators, because otters, and defend the group’s territory against incursion by other otters, also because otters. (Turf fights can actually get really nasty and result in dead otters, because eighty-pound murder-machines.) The previous year’s babies will still get fed after begging if they haven’t caught enough to feed themselves, but they’re more or less fully-contributing members of the pack by that age. Once the babies reach sexual maturity (2-3 years), they either leave the group to find mates of their own or, if the alpha pair get too old to breed or fall victim to rain forest mortality rates, replace them.
Did I mention these assholes get up to six feet long? Because they do.
They’re okay with human contact in areas where they haven’t been hunted or harassed extensively, but they play rough, so trying to frolic with them is not recommended. Trying to domesticate them is a fool’s errand, because they’re six-foot-long pack hunters, and they’re not above biting the shit out of you.
They can thrive in captivity; assuming an appropriate enclosure and companionship are provided, they’ll breed readily and can live over twice as long as they do in the wild. A few rescues that are basically otter halfway houses have even successfully raised orphaned kits in semi-structured environments and had them go on to behave more or less normally in the wild.
Let’s face it, it’s not exactly a high bar to clear.