No, I don't think you can stretch it. George looked at Harry. 'I think we should be going', he said. I can suss that George is talking when it is stated this way, but I don't think a person can look a speech.
'Complete sentences' do not require a period; a semicolon can often substitute.
Does written dialogue always have to use said, spat, screamed, etc? No, not as long as it is obvious who is talking. Furthermore, a good writer shows the emotion in the dialogue itself, rather than just by telling us, via the verb, that the speaker was, for example, angry.