Why spinning particles break a universal limit—but somehow obey it anyway

An accelerated observer experiences the vacuum as a hot gas (the Unruh effect). For simple particles, this thermal medium has a shear viscosity-to-entropy ratio locked at a fundamental minimum—the KSS bound. Testing this for spin-3/2 fermions yields a puzzle: negative viscosity and negative entropy appear, yet their ratio still saturates the bound. Two different calculation methods flip the sign of entropy, suggesting the negativity reflects a subtle feature of how spin couples to acceleration rather than a violation of universal physics.