Meditation, probably. Take the edge off the Eritrea policy of torturing their prisoners, hopefully.
No, that was Meditation, not Masterbation.
Geeze, a lot of you folk are destined for stinky, sticky cells and sore groins, apparently.
I could see the guards now, "Oh, by Allah, not again! Achmed, go get the mop, I'll flay the skin off this infidel's back for spilling his seed!"
(Eritrea is about 50/50 Muslim/Roman Catholic [http://en.wikipedia.org/wiki/Eritrea#Religion], so in masturbating in a Eritrea prison, you probably wouldn't be the only thing feeling oversensitive.)