The great nineteenth-century preacher Henry Ward Beecher, in a sermon, likens thankfulness to a search for iron filings.  If you hand me a dish of sand, he says, and tell me there are particles of iron in it, I can search through it with eyes and fingers and turn up nothing.  Yet, take a magnet and pass it over the sand, and the iron filings will leap into the air.  That's the way of a thankful heart, Beecher says: it searches out God's blessings, as though with magnetic powers of attraction.