"Smell A Rat"
Context: Though the expression "I smell a rat," to indicate suspicion, has been traced back in English to Image of Hypocrisy (1550) (I, 51) by John Skelton (1460?-1529), no one has ventured an opinion about its origin. Perhaps someone, sniffing a foul odor, suspected a dead rat in the house. Said the poet laureate of both Oxford and Cambridge: "If they smell a rat / They grisely chide and chant." Sancho uses the expression while discussing with his master how he has been tossed in a blanket and the Knight has slashed the wine skins. He rejects his master's explanation that in the inn "all things are ruled by enchantment."
. . . "I believe it," quoth Sancho, "had my tossing in a blanket been of that kind; but sure 'twas the likest the tossing in a blanket of anything I ever knew in my life. And this same innkeeper, I remember very well, was one of those that tossed me into the air . . .; so that after all I begin to smell a rat, and do perilously suspect that all our enchantment will end in nothing but bruises and broken bones."