I have volunteered as a prison teacher and my job was to teach prisoners in a school. The prison is totally another world and you will begin to wonder how they survive in such conditions. In this prison, everything, including drug use, gambling, prostitution, cultism, and others, exists. I have never seen people gambling since I am not allowed to visit their cells, but I have firsthand information that they gamble with money, food items, clothing, bed space, and anything that has value. You can gamble with a comfortable sleeping space and sleep on the floor if you lose. I might not be surprised that gambling exists in the afterlife 
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I'm not really surprised with this. However, is this happening in all the prisons around the world? If this happen in almost all the prisons, the prisons never function as it should be. Instead of changing to be a better one, they probably become worse poeple while in prison. It's no wonder they can gamble in prison because things like drugs or sex also exist. By the way, teaching them will be useless if they are still involved with those activities, right?.Smuggling something from outside to inside of prisons is usual things to do so that will not be a problem for them. Bribing the guards is also help them to get what they want from the outside.
This is a common fact. It's very unfortunate that prison guards are still bribeable, so anything can still be done in prison. Even gambling with anything, it is quite possible as long as the prison guards are easily bribed.