Why do mentally retarded people LOOK retarded?

[kayaker]

@Rayks_Marcial

Well, during the golden age of cinema female movie stars liked to look and talk retarded.

Care to elaborate?

[Dinsdale]

@Ulfreida

I have often reflected, not exactly on the OP, but on the opposite – how do I know someone is unusually intelligent, or unusually interesting, without them opening their mouth. …

Basic physics. Light travels faster than sound. Hence, many people appear intelligent until they open their mouths!