In July 1999 I was attending the celebrations for the "Festa del Redentore" in Venice, when fireworks are launched from the waters of the Grand Canal in front of St. Mark square. Seen from a boat, the fireworks exploding gave a very vivid impression of "coming towards us" at the moment of the explosion, when we know that - instead - they blow up isotropically in all directions of space (with some corrections due to gravity).

These notes (28KB gzipped postscript) explain that the image generated on the retina of the viewer from a rigid configurations of "fireflies" coming towards the viewer is identical to the image generated by a (non-rigid) configuration of fireflies exploding isotropically from a point in space (the center of the explosion). See it for yourself by attending the celebrations! (well worth especially if on a large boat with food, music and 30 or so noisy friends).