In Zoega or where ever - it mentions the "Hough" tendon, which seemed to imply to yours truly that hey were strung up upside down in a humiliating way, treated like oxen/pigs for the slaughter, they do so hang up animals that way,
As for the "í örskotshelgi  I saw that as - sort of nearish   and the rocky mound suggested that it would be a kind of vantage point, where-from they could observe and point to one another the different parts of the Farmstead, there are some rocks hard to shift and perhaps they knew of one such.
 
In my effort I made mention of the blood running into their eyes due to the force of gravity  well the strain  of this treatment  - being hung upsy down would make the blood run that way and make their eyes water too, I must be heartless for I ended up  thinking "oh what a gay day"
Kveðja Allir
Patricia
Never mind the Rock - try to shift a tree - that is bad enough - the whole world is holding onto the roots