From “Tantalizers: A Book of Original Logical Puzzles” (1970)
Montmorency left as one morning at Iffley Lock and returned three hours later, chased by men waving sticks and frying pans. He leapt into George’s arms with a look which meant: “Save me from this unjust world”; but we are used to that by now. We were told (and in such coarse terms!) that he had been down as far as Folly Bridge, taking two hours about it, and tangling with three fishing lines, two Primus, stove, and a towrope. After a few minutes nap, he started back. This time he searched for rats in picnic baskets, licked the faces of people asleep in the sun and bit their air cushions. He had followed exactly the same route each time, never doubling back or crossing his own tracks.
George was silent during lunch. Then he suddenly posed us a question. “It is obvious”, he said, “that Montmorency passed through each spot on his route twice. But did he pass through any twice at an interval of exactly 2 hours?”.
That had us.
Did he and, if so, how many? Or is there no way of telling?
This puzzle is from the book Tantalizers (1970), but I have not found a corresponding Tantalizer puzzle originally published in New Scientist.
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