This is Aristolochia rotunda, or "fat hen." It's a common plant, native to southern Europe. It doesn't look like anything special, but scientists recently discovered that it has one of the most wacko breeding strategies in all of nature.
When you learn about nature, you constantly have to pause to wonder if the naturalists are playing a prank on you. Things just keep getting crazier. For example, it's pretty insane that spiders liquify their prey and then suck up the juices. But we learn that when we're young, so we get used to that fact.
There's another layer. Spiders are not the neatest eaters, and even they can't digest everything. When a spider is done with a insect, there is usually a little goo left over. There are also insect bits that ooze out when an insect is being eaten by a praying mantis or other arthropod. These are free calories, available for whatever scavenger shows up. Evolution being what it is, eventually, a specific kind of scavenger showed up. A specific class of flies eat the freshly-chewed bug bits that come from these feeding predators. The endeavor is dangerous. Whatever fly shows up might end up on the spider's menu. But meat, in whatever form, is a rich source of nutrition, and seems to make the risk worth it.
This is where it gets insane. These scavenging flies are quick to show up to anything that smells like a fly being eaten by a spider. Plants who depend on flies to propagate their species, could use a reliable fly like that, but they can't catch and kill insects in order to attract the flies. One plant doesn't need to. When it needs to breed Aristolochia rotunda puts out a combination of scents. These scents, when brought together, mimic the smell of an insect being crunched by a spider. Attracted to the smell, these special flies show up and find no juicy insect goop, but they do get thoroughly covered with pollen. They then proceed to the next plant, get duped again, and pollinate the new plant.
[Via The Betrayed Thief.]