This charming French optical toy dates from around 1993. It was designed by P. P. Parmentier, and is an example of the so-called 'picket fence' animation. A picket fence you will remember, is constructed of reasonably wide, vertical planks of wood, with fairly thin gaps between them.
The picture card - the cowboy in this case - has a number of alternative images printed on it, in the form of very thin vertical stripes. In front of the picture card is a piece of clear plastic, which has vertical black stripes printed on it with thin gaps, where the plastic remains clear, in between.
When the pendulum is made to swing, it causes the plastic card to move slightly from side to side. We can only see the card through the thin strips where the front plastic card is clear, and thus we only see one of the images at a time. As the plastic card moves from side to side, we see the different images on the card, and we get a lovely animated effect.