Luther's Thurmerlebnis (experience in the tower) in the original German (I'm sure you can get the reference online and use Google's translation tools - however inept - to get to the gist.) In additiion to several references expressing the centrality of the Devil to Luther's theology (filth, blackness) he states a specific fear that he(Lucifer) will be thrown into his anus where he belongs.
Real pathos.
So? A lot of people were superstititous and ignorant about such things at that time. Not just Luther.
How can a person conceal himself from the jinn when in the toilet?
;-)