By the KSS bound, the ratio of eta to entropy density of these substances is lower bounded by one over 4pi. The stress-energy tensor of an ideal one of these substances is rho plus p times (-5[1])a product of 4-velocities plus p times the metric tensor. In the rest frame, a “perfect” one of these substances is parametrized by its isotropic pressure and energy density, and therefore has a diagonal stress-energy tensor. By definition, these substances have zero shear modulus, meaning they cannot undergo shear stress without deformation. (10[2]-5[1])Many Bose–Einstein condensates act like an idealized (10[1])“super” one of these (10[1])substances that move without dissipating energy. The Navier–Stokes (10[1])equations are central (10[1])equations in the “mechanics” of, for 10 points, what substances that can flow, including liquids and gases? ■END■ (10[2])