Algodoo

Two large dots are slowly flashing black and white. Are they flashing together in synch, or are they alternately flashing out of synch with each other? CONTEXT IS EVERYTHING when it comes to seeing what you think you see!

Edit - Just letting you know that I do not do anything funny with Thyme script or anything else when the black/white squares are moved away from the dots. The two dots are always flashing together in synch. In other words, they are black at the same time and white at the same time. But when you move the black/white squares behind the dots, they are now situated in a different "context", and it's the context that makes your brain think that they are flashing alternately. If you are not convinced of this, then cut two holes in a thick sheet of paper or cardboard the size of the two dots and separated by the same distance on your monitor. While the dots appear to be alternately flashing, hold the paper or cardboard up to your monitor so that the dots can be seen through the holes, and the black/white squares can no longer be seen.