Pisaura mirabilis, also known as the Nursery Web Spider, or nuptial gift-giving spider, or a Fishing Spider, or a Raft Spider, is one of a widespread family of wolf-spider-like arachnids well known for their ability to run across water or dive into it after fish and tadpoles, and only build webs for their egg sacs to hatch in once they get tired of lugging them around. And given those eggsacs can be so big the spiders have to run around on tippy-toes to carry them I imagine they get tired quite quickly. (By another odd coincidence, the spider genus Nukuhiva I mentioned in completely unrelated context elsewhere is another Pisaurid.)
But before they have any eggs to care for they have to breed, and to do that the male has to cope with a female potentially more interested in food, rather than pork sword.
Here's a photo of one nervously handing over a gift-wrapped pre-coital bribe.
Others don't get that far. They bring her a gift-wrapped meal alright, then keel over dead as soon as she looks at him anyway, assuming what we shall refer to as the X-P posture. But he's faking it.
Thus, the object of his desire thinks "Hmm, shall I eat him, or hump him.. oh, he's dead. Hey,
To quote from one of the papers on the subject
When entering thanatosis, the male would collapse and remain completely motionless while retaining hold of the gift so it was held simultaneously by both mates. When the female initiated consumption of the gift, the male cautiously ‘came to life’ and initiated copulation. Death feigning males were more successful in gaining copulations, but did not have prolonged copulations. We propose that death feigning evolved as an adaptive male mating strategy in conjunction with nuptial gift giving under the risk of being victimized by females.
Actually, Pisaurids don't just play dead to get some, they also play dead to avoid getting killed - see this account for an unfortunate Dolomedes that didn't get away.