The celebrated frictionless flow properties acquired by liquid helium at very low temperatures have long been known to vanish abruptly if the velocity of the liquid exceeds a certain critical value. The physical mechanism underlying this breakdown of the superfluidity has, however, remained an enigma, and it is pleasing, therefore, that a possible solution to this important and long-standing problem has now been proposed by K.W. Schwarz of IBM (Physical Review Letters 57, 1448; 1986).