We extend the phenomenology of mixing and oscillation to U (1) vector bosons. Extracting constraints on kinetic mixing between a new U (1)' gauge boson hiding under the Standard Model Z boson resonance requires the formalism of non-Hermitian two-point correlation functions at 1-loop order, whose phenomenology is reminiscent of neutral kaons in the SM. After updating the collider constraints on Z' bosons with kinetic mixing in the narrow mass window around the Z boson, we discuss the novel phenomenology of Z' regeneration and motivate searches for displaced vertices from Z' decays. The time evolution of the highly mixed state also exhibits the quantum Zeno phenomenon.