Genesis

The characters' motivations are unreal and Carol Rossen is particularly misused as a female scientist who lets every other character buffet her around the plot like a pinball with no will of her own. The idea of the police officer downwardly mobile in his career getting scared into a catatonic state at the sight of an unregenerated alien might have been a good one, but it is poorly acted and directed and probably originally poorly written.

This episode gives us another glimpse of the aliens in their true form (See also "The Spores" in the second year), but it is not much, just a trunk with short appendages. So when these aliens take human form, they must increase in size as well(?).