Although most laymen know of the canary as a common animal in the coal mine, this animal was a tool; not a superstition. It was used to monitor oxygen in the mine. But there was, and still is, an animal that holds some lore for the miners. Rats were mentioned by all four participants. George Monas stated that "if the rats leave an area, trouble [was] coming." All the others had variations on this same theme. Also noted by Nick Massini, was the idea that the death of a mule was more serious than the death of a man.
The rats involved in the coal mine were just like the rats that would leave a ship if it were sinking. In Elliot Oring's collection of folklore discussions, this comes up in the discussion of fisherman and their folklore as part of the occupational folklore.