Can you tell me how many black dots there are?
If you have tried counting the black dots, you will see that it is not possible to do so.
This optical illusion is called the scintillating grid illusion and makes you believe that the dots located between two lines appear and disappear. If you focus on a single point, it disappears.
Discovered by E. and B. Lingelbach and M. Schrauf in 1994