Yes,..interesting. It is not too dissimiliar to a condition called 'pica' which is what some women expereince during pregnancy. It is a craving for clay like materials. I am assuming you are lying down on the ground or at east sitting down with arm contact on the ground hence a likelihood of contact dermatitis whcih would explain the redness or otherwise you are living in a fertile area with a lot of red soil normally high in Ferrosol concentration.

The shaking well that is the easy bit. I would relate this to the sheer excitement of one feeding themselves with a percieved delight. Like the feeling of excitement we get when we are doing something naughty or taboo.

I must say thank you for a great question my friend and it's a delight to answer - haha now my typing arm is shaking with delight!!