Because of this persistence, we can't tell where one flash ends and the next begins. Instead, we perceive a continuous light. If, when you spin the zoetrope, you look over the top of the drum at the drawings instead of looking through the slots all you will see is a blur. The illusion of motion is gone. The slots of the zoetrope simulate flashes of light, creating a strobe.
Persistence of vision is a stroboscopic effect.
The images you see must be interrupted by moments of darkness in order for the illusion to work. The Phi phenomenon is a result of human instinct. Our brains strive to make meaning from what we perceive. When we see different images close together our brains quickly create a relationship between them. The metamorphosis of an umbrella into a mushroom makes a certain kind of sense, even though this is not something you would ever see in the real world.