Just as legitimately nice restaurants do not require any further comment, the phrase of stones hugging one another overnight gives us an immediate and clear impression even though we must never have seen such a thing ever before.
We all know too clearly where the stones are seated and what they really are. To get a clearer picture of what it means, you may need to be still up until the middle of the night. A tired husband gnashes his teeth in his sleep at the corner of the room next to the younger kid rolling up like a ball. The elder one sleeps spread-eagled on the floor. A look at the sleeping family may give you a hint at the meaning of the stones hugging one another overnight.
A long time ago, people before us would heat stones up in a fireplace so that they can keep one in their arms to stay warm overnight. They would shily hand over a heated stone to a loved one. I sometimes feel confused about whether I am being a cold-hearted stone drying up over time or a stone is being me getting cold. This is where this poem works out. As it is in the middle of winter, we may need to turn even our heart into a warmly heated stone on the floor.