When people think of the worst episodes of The X-Files, it's pretty much a given that this is going to be listed among them. Episodes that sideline Mulder and Scully to talking heads automatically tend to be thin in substance; this was largely where "Space" failed back in season one. To that episode's defense, it aired very early in the series's run, and despite being poorly executed, it tossed around some relatively unique ideas. This episode fails because it's just crap.
And even then the premise could have worked, had it been approached from a comedic angle. Having aired amidst Darin Morgan's trinity of episodes, which were all quite hilarious in their own regard, it's quite surprising the writers opted not to do this. Instead the case is approached with the same level of seriousness as any standard monster-of-the-week, which is unfortunate because the case itself is utterly silly.
War of the Coprophages, which aired several months earlier, was also founded on a ridiculous premise, but succeeded as a send-up of classic sci-fi and also a self-parody of the series. There is no such attempt at cleverness in Teso dos Bichos. An artifact is stolen, a curse is invoked by means of some hallucinogenic concoction, employees at a museum die under mysterious circumstances, and the culprit leaves behind a trail of dead rats. The script initially sets us up to believe we're dealing with a p'd-off jaguar or some relative of the animal kingdom. Wrong.
Instead we're treated to a legion of housecats with sticks up their arses. Perhaps the writers were treated to some of Dr. Bilac's yaje in pre-production. Either way the result is an episode that should never have made it onto the screen, especially at such a peak era of quality in the series. Even episodes from the much-derided final seasons don't quite sink to this level of garbage. 3/10.