(Please see this gif here) The device seems to spin at a very high speed and we can see the wings of the device turning slowly (IDK due to some illusion). We can encounter this phenomenon in spinning fans too.
My question is, why am I able to see the wings of the device on those particular points? Why am I not seeing them in other points? Does the device tend to slow down at those certain points?
I'm not a Physics grad or anything. Sorry if the question is trivial.