The cube appears to flip so that the red dot is sometimes inside, and sometimes outside the cube.

When you look at this 2D drawing, your brain automatically visualises it as a 3-D cube. But this drawing does not give enough information for your visual system to know exactly which face of the cube is at the front.

This ambiguous cube shows us that anything we see is just a ‘best guess’ by our visual system. Your visual system has a hypothesis that the cube is at one orientation, then for some reason suddenly another hypothesis is favoured and the cube flips. We never see both orientations together because our visual system must decide which hypothesis is favoured.