Why would someone eat their own semen?

weird question, I know, but I've been looking for the answer elsewhere and I can't seem to find it. I've been reading a book where a guy has a habit of eating his own semen (it's called Homunculus if you were wondering). I'm sure this has some symbolic meaning or is a byproduct of some psycho-ual phenomenon, but I was wondering if anyone had an actual explanation, since it would appear others have also done this (just do a google search). Thanks.