An old technique, where you “zoom in” your subject while the shutter is open. Typically using shutter speed of 3 to 6 seconds.

Several shots must be taken before producing one that is “presentable”, sometimes the results can be quite surprising.

These 2 pictures where taken with an 18-105mm lens on my Nikon D90, 3 seconds shutter speed, dock of Place Datura, Ile-Perrot.

François