Thanks Walterick and Lava Lamp. Photo101, it is easy in theory: just use a shutter speed slow enough where you can zoom while it is exposing. I'd say about 1/15 or slower, but it's been awhile - would be ideal to use about 1/4th with the camera on a tripod. It is hard to get right. As BoingBoing pointed out, maybe as long as the subject is recognizable it has a good chance of working. I think the yellow against the black background really helped the cab.

GB