Why am i able to see the blade in that particular place? Why not in other places? (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.
 A: There a lots of things that go "weird" when you record something with a digital camera. Specifically to your question, you're recognizing the stroboscopic effect (Wikipedia), which happens when you "sample" light with a camera at a specific frame rate. You can see "frozen" motion and even "backwards" motion from different frame rates as shown below:

Another effect in that clip are the wings changing in size because of rolling shutter. Aliasing is another interesting effect, but not seen in the gif. Have fun exploring!
EDIT:
You can even see this inside too, if you have an illumination source that strobes (most things LED, fluorescents sometimes). It will look like this:

EDIT2: 
For continuous light, it appears there are some effects that can be seen with the naked eye. See https://en.wikipedia.org/wiki/Wagon-wheel_effect#Truly_continuous_illumination
A: Vision may seem continuous but it's not. The eye captures a couple of frames per second. If the blade rotates at a rate where every frame has the blade in the same position it looks like the blade isn't moving. 
