More on the first-order thermodynamics of scalar-tensor and Horndeski gravity.Two issues in the first-order thermodynamics of scalar-tensor (including "viable" Horndeski) gravity are elucidated.  It is shown that the formalism holds thanks to the almost miraculous fact that the constitutive relations of Eckart's thermodynamics are satisfied, while writing the field equations as effective Einstein equations with an effective dissipative fluid does not contain new physics.
THERM