Besides the answer already given, I would think some men would want to take full advantage of an unusual situation where a nubile girl’s imminent death was known and sanctioned by the community – no risk of pregnancy, and no risk of direct retribution, as her man/master was dead. (True, any slave-owning society will tend to produce other opportunities for “consequence-free” sex, but still, I’d guess this was a factor in the development of the ritual.)
Not to mention that they were all pissed out of their brains on drugs and alcohol
I think it’s a real tribe … some of your answers were close, but this particular tribe dug long trenches and buried everyone like it was a parade on the way to another world.
The king and his wives and his children and everyone in the village with poison I think and the men that buried them would be the last to fall by falling on their spears. They knew ahead of time that this was the kings wishes of how to get to another world.
The only way they could possibly know about them is that they found the buried remains with the horses, wagons, people and gold and silver in the long trenches.
I’ll keep looking 
Well, one would think any possible life essence build-up might get wasted in the process of, I don’t know, KILLING the girl, but I’m no Viking loremaster. Who knows ? Maybe she did show up in the afterlife full of, erm, spunk, and ready to spread it around.
The Viking afterlife was some kind of fucked up, wasn’t it ? 
Crass jokes aside, again, thanks for the enlightenment.
Huh. So, it didn’t occur to anyone else that they thought the girl might like a little action on her last few days?
If she was a thrall, nobody cared much what she cared for. Sad but true (even if Nordic slavery was not *quite *as horrible as the chattel slavery Americans are familiar with)
A propos of nothing, but in the interest of sharing dark historical ironies, the spread of Christianity into Scandiwegia actually *increased *slavery there in spite of its purported fundamental message of brotherly love and equality : preachers said it was Wrong to enslave one’s fellow man, which meant that thralls taken as the business-as-usual part of internecine warfare or debt-induced bondage were now frowned upon.
Foreign slaves however, not being one’s fellow man since they were damn dirty foreign apes worshipping heathen gods were now all the more A-OK and as-of-then still quite rare. Cue the raids solely dedicated to enslaving Slavic non-Christians, for profit and in numbers far exceeding the number of thralls that had been taken before (though I hasten to add that one possible reason Vikings didn’t take too many foreign slaves before was that they killed folks outright. The smallest of blessings, then, perhaps).