       else /* Material -> Air */
         incident_ior = triangle.material.ior;
       eta = incident_ior / transmitted_ior;
+      shininess = 0;  // Hack: indicate mirror reflection
 
       const float3 direction = ComputeTransmissionDirection(
           normal, ray.direction, eta, curand_state);

                                             const float shininess,
                                             curandState* curand_state) {
  float3 perfect = ComputePerfectReflectionDirection(normal, incident);
  return ComputeRandomCosineWeightedDirection(perfect, incident, shininess,
                                              curand_state);
}

      ray.color *= triangle.material.specular_color;
      ray.direction = ComputeReflectionDirection(normal, ray.direction,
                                                 shininess, curand_state);
    } else if (random <= threshold[2]) { /* Transmission */
      ray.color *= (1 - triangle.material.dissolve);
      ray.direction = ComputeTransmissionDirection(normal, ray.direction, eta,
                                                   curand_state);
