The suggestion that the shells of planetary nebulae may be formed at the interface between two stellar winds of different velocity (“Not with a bang, but a whimper”) (Kwok, Purton and FitzGerald, 1978, Astrophys. J. 219, L 125) is investigated using the ‘beam scheme’ (Sanders and Prendergast, 1974, Astrophys. J. 188, 489) adapted to a system with spherical symmetry. Initial conditions include the remnant wind from the red giant phase and a highspeed wind from the hot nucleus ( (two tests), v = 103km s−1). The collision began at a radial distance of 200 AU. A third test at 50 AU indicated that the end result was insensitive to the details of the transition from one mass-loss mechanism to the other.