OK. Now, don't scream, "sacrilege". Let me explain...
More than 100 years ago in Italy, people really would place the Nun and Priest into their beds to warm things up. The Suora e Prete (Nun and Priest) was the name of a device used to warm the bed and blankets just before bedtime. In northern dialect, they might be called Frà dël let, or Bed Brother.
They were often used until the early 1900's, and perhaps even later on in poorer parts of Italy. The Nun, or scaldaletto (warming bowl), was a removable round bowl with handle, into which hot coals (with ashes to slow down their cooling) were placed. Placing hot bricks in place of the Nun was also an option. Wealthier folks could afford rocchetti--small cylindrical containers filled with compressed coal dust. They were heated in the fireplace and lasted a lot longer than loose coals and ash.
The Priest constituted a frame that housed the Nun along with its hot embers, holding sheets and blankets well above the coals to prevent them from scorching or bursting into flames entirely. Sometimes the Nun had a lid with decorative perforations which allowed the heat to escape. The Nun and Priest also helped dry the damp sheets--a common problem in the cold and damp of stone houses during the winter months.
What are the roots of the name? Many consider the draping bed coverings to look like the draping of a nun's hood. Why "Priest" then? With Italians' tendency to be shockingly irreverent, we can only guess. Perhaps there is a reason the priest is on top... of course, I mean to hold in the heat of the Nun under "him". Wait... I'm getting myself into trouble here....
The interesting thing is, the Nun and Priest is still being made today, albeit in electric versions. When considering the thick stone walls and dampness of old Italian houses, this contraption might seem like a very good idea to warm up the bed on a cold windy night.
Very common in Italian antique stores and flea markets, many people have taken to finding new uses for the Nun and Priest, especially as decorating objects.
The Monk, a Close Cousin...
Another tool to heat the bed was il Monaco or also Mariteddu (the Monk), a kind of terracotta amphora that was filled with boiling water and placed under the covers. The rather thick, heavy ceramic would retain heat for long periods of time and release it slowly, creating a gentle warmth under the covers. Unlike the Nun and Priest which warmed the bed before you got in, the Monk could be kept in bed during the night with you.
Oh no... here I go again. I'll stop now.
This might also interest you...
Italian Warmth from the Poor Mans' Hearth: Il Braciere, the Brazier