Chaste women place their beds upon bricks to deter the rather short fellows from attaining their sleeping forms. Some of the causes are sleeping without adequately covering the body especially women and eating in bed. Eight hundred years later, Thomas Aquinas lent himself to the ongoing discussion, stating, "Still, if some are occasionally begotten from demons, it is not from the seed of such demons, nor from their assumed bodies, but from the seed of men, taken for the purpose; as when the demon assumes first the form of a woman, and afterwards of a man; just so they take the seed of other things for other generating purposes. He stated, "There is also a very general rumor. The Trauco is said to be responsible for unwanted pregnancies, especially in unmarried women. Gradually the victim's health deteriorates and in some cases develops suicidal tendencies. Let your fascination get the best of you and keep reading about these people who claim to have had sex with the Devil. The reason for this is ultimately unknown but the most common explanation is that this prevents one from acting out one's dreams. It can be seen or heard in the nightmare and a heavy weight is felt on the chest. Add to this the common phenomena of nocturnal arousal and nocturnal emission , and all the elements required to believe in an incubus are present. In Swedish folklore , there is the mara or mare , a spirit or goblin that rides on the chests of humans while they sleep, giving them bad dreams or " nightmares ". This is similar to depictions of revenants or vampires and a spirit taking deceased corpse to cause some mischief. They also share the hole in the head detail and water dwelling habits of the Boto.