Answer:
a quantum fluctuation
Quantum Physics is the physics of the atom and the particles that make up atoms, and they behave according to a different set of rules than large objects like people.
So a quantum change could be any sort of change at the atomic and subatomic level, like an electron's direction of spin, its velocity, or its probability of being in a certain location. Electrons are in many places at the same time, spinning different ways at different speeds. It's only when we go to measure one of these properties that it "snaps" into one of its possible locations.