A priest and a nun are on their way back from the seminary when their car gets stuck in heavy snow.
There's no point trying to go any further now, we should wait until the morning before moving on and stop in the nearest B&B tonight, but unfortunately on entering they find it only has one room available.
The priest says: "Sister, I don't think the Lord would object if we spend the night sharing this one room. I'll sleep on the sofa and you have the bed."
"I think that would be fine," agrees the nun. They prepare for bed, say some prayers and settle down to sleep.
Ten minutes pass, and the nun says: "Father, I'm very cold."
"OK," says the priest, "I'll get a blanket from the cupboard."
Another ten minutes pass and the nun says again: "Father, I'm still terribly cold."
The priest says: "Don't worry, I'll get up and fetch you another blanket."
Another ten minutes pass, then the nun murmurs softly: "Father I'm still very cold. I don't think the Lord would mind if we acted as man and wife just for a night."
"You're right," says the priest. "Get your own blankets!"