In my last house, built in 1929 with standard wood-burning masonry fireplaces, a heat-exchanging insert had been installed in the living room fireplace. The insert covered the entire opening of the fireplace, and unbeknownst to me, the cavity inside the fireplace had been filled with granular insulation, surrounding the smaller insert. A squirrel fell down the chimney, and sunk into the insulation like a dinosaur in a tar pit. He tried to dig himself out, and my first clue that something was up was a small pile of the insulation spilling out of a corner of the fireplace. I had to pull out the insert and dig out the squirrel. Happy ending for squirrel, who was released in the adjacent park. Not so happy ending for me, who spent hours dispensing with the insulation, which flowed into the living room like sand from an hourglass.