He is said to have trapped cat when a situation seems suspicious, as if there were a trap or something hidden. Contrary to general opinion, the sentence was not coined by Schrödinger, but it has some centuries old. During the Middle Ages it was customary for travelers carry their most valuable belongings in some tassets or bags of skin hiding among their clothes; still, thieves were attentive and when they discovered some used the hidden cat expression to designate the victim who thought assault. Assumes that cat is because these bags were made with the skins, soft, cheap and easily obtainable. and time shifted the hidden by locked, when the use of the wallet is lost in the memory. See have enclosed cat, pelagatos.
