I came across this image the other day. I had heard of the Water Chestnut (Genus Trapa .) and that it could be used as a caltrop but had not seen them in such detail.
It is a pretty fearsome looking object and it is perhaps no surprise that one of the alternate common names is “Devil Pod”.
I remarked to a friend that they looked like something from Aliens and his comment was that they were not sexual enough for that. I pointed out that they do look a little like the Uterus and Fallopian Tubes diagrams in biology textbooks.