Quantum-locking

Quantum-locking is a feature gained by species through evolution. The concept is that is a creature can move incredibly fast, it can evolve into being "quantum-locked".

If a creature is quantum-locked, then they are turned to stone whenever they are observed. However, if the observer turns away or blinks, they take their eyes off the creature, allowing the creature to move for that split second. If two creatures are quantum-locked and are together, they must becareful and be sure to cover their eyes before they are turned to stone. If they don't, they risk seeing each other, and being that they are both being observed by the other, they would be trapped in stone form.

One species that had evolved into being quantum-locked was the Weeping Angels.(DW: Blink)