The physicist Robert W. Wood could never resist the opportunity for a practical joke. While staying in Paris he found that the apartment below his was occupied by a woman who kept a pet tortoise in a window pen. Seeing the rich possibilities of the situation, he went out and bought a number of tortoises of his own in graduated sizes. Then he rigged up a collecting device using a broom handle – and waited. As soon as the woman left, he leaned over his balcony, caught his victim's reptilian friend, removed it and replaced it with one that was slightly larger. Every day he repeated this bizarre substitution until the woman, in alarm at the sudden spectacular growth of her pet, went to Wood for advice. He suggested she contact the press. And so, in a very short time, a bevy of newsmen were onto the story, measuring tapes at the ready, issuing daily updates on the animal's remarkable progress to an expectant public. Where would it all end? How big would the creature grow? Only Wood knew. The day after introducing the largest member of his collection, he threw the process into reverse. And, as fast as it had expanded, the tortoise now shrank, down and down, until it had returned to its original size.

Another trick perpetrated in the French capital was due to the physicist Jean Perrin (who won the Nobel Prize for his work on the thermal motion of molecules). Perrin mischievously packed a powerful aviation gyroscope into a suitcase, set the gyro spinning and left the suitcase at a Paris railway station. An unsuspecting porter picked up the apparently forgotten luggage, marched off with it and then made the mistake of trying to turn a corner. The case – or, rather, its contents – refused to follow. When the porter attempted to force the unwilling bag to point in the new direction he wanted to travel, it simply rotated on its handle at a bizarre angle and twisted the bewildered man's wrist. Dropping his strange load in alarm, the porter ran off yelling "The Devil himself must be inside!"