**Lab 1:** Alice (inner observer) measures a quantum coin. If heads, she prepares a spin-1/2 particle in state $|\!\uparrow_z\rangle$. If tails, she prepares it in $\frac{1}{\sqrt{2}}(|\!\uparrow_z\rangle + |\!\downarrow_z\rangle)$. - Alice sends the particle to Lab 2. - **Lab 2:** Bob (inner observ