THE INNOCENCE OF FATHER BROWN
in a shop-front went by him like a mere flash; yet he went back to look at it. The shop was a popular greengrocer and fruiterer's, an array of goods set out in the open air and plainly ticketed with their names and prices. In the two most prominent compartments were two heaps, of oranges and of nuts respectively. On the heap of nuts lay a scrap of cardboard, on which was written in bold, blue chalk, "Best tangerine oranges, two a penny." On the oranges was the equally clear and exact description, "Finest Brazil nuts, 4d. a lb." M. Valentin looked at these two placards and fancied he had met this highly subtle form of humour before, and that somewhat recently. He drew the attention of the red-faced fruiterer, who was looking rather sullenly up and down the street, to this inaccuracy in his advertisements. The fruiterer said nothing, but sharply put each card into its proper place. The detective, leaning elegantly on his walking-cane, continued to scrutinise the shop. At last he said, "Pray excuse my apparent irrelevance, my good sir, but I should like to ask you a question in experimental psychology and the association of ideas."
The red-faced shopman regarded him with an eye of menace; but he continued gaily, swinging his cane, "Why," he pursued, "why are two tickets wrongly placed in a greengrocer's shop like a shovel hat that has come to London for a holiday? Or, in case I do not make myself clear, what
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