Photo by Ch'ien C. Lee
Pitcher plants are generally carnivorous, capturing insects in deep, liquid-filled bowls. Well, like other carnivorous plants, they grow in mineral-poor areas, so this is how they get many of the nutrients they need. But here's an article about pitcher plants that have evolved to serve as a toilet for shrews.
Jerry A. Coyne explains it better than I could, but basically, the shrews don't deliberately defecate there. They're just attracted by a sweet substance on the "lid" of the bowl, which they can best reach by sitting on top of the bowl. So, when nature calls as they're licking away at their treat,... the bowl is perfectly positioned.
Neat, huh? I've always been fascinated by the wild variety of solutions that living things have evolved over so many millions of years.