It isn’t easy when they appear to be moving backwards!
Your eye-brain system has a limit on the `frame rate’ it can process, which is why films look continuous rather than jerky. On a car wheel revolving at a certain rate, after one `frame’ the next spoke will be at a point just behind where the previous one was in the last frame. Your brain will process this not as the spokes travelling too fast to see but as one spoke travelling in the opposite direction,
It is easy to count a small number of spokes if they are not revolving too fast. But it is tough to count spokes on a bicycle even it is standing still.