Deep shaft miners used to take tiny songbirds to work—probably still do in some places. The reason has less to do with chirping than the fact that songbirds are delicate; a fact easily confirmed by any pet owner who’s found her feathered friend face down on the newsprint. Turns out that domestic weakness is an asset in deep shaft mining. The little fellas have tiny respiratory systems and remarkable but equally tiny brains. Said plain, toxic gases are sometimes released