well, all i know is that every time i've seen a man scared or startled, he ends up with his dick buried somewhere in his stomach fighting for space with his nuts....
i do know that some men do get an erection when they aer frightened jusrt liek some women who have been raped get this guilty feeling because they have gotten wet adn been somewhat stimulated physically while being violated while in their minds and hearts they are tearing up and they get wet while they are frioghtened... so yah