What a fantastic idea!

I think every child has done this at some point in their life... created a deck of flash cards with slightly different images, which, when the deck is fanned, appears to be a motion picture.

Some advertising company has used this premise to create "motion picture" advertising inside darkened train tunnels. As the train passes each lit advertising panel, part of the message is delivered, and over the course of the trip, the message unfolds in motion pictures.

Hmm, I wonder how that works when trains are travelling in the opposite direction?