I'm sure this is a clip I've been looking for for over 40 years - at high school we were shown a film in English class, and at the end of it, possibly the tail end of an earlier recording on the videotape, Peter Ustinov came on-screen talking about the way the shape of your mouth and face changes when you speak another language ... the teacher switched it off, muttering something about "This is boring, no need to leave this running", and I'm there saying "No, please, let's see what else he has to say", but I was ignored.
I have sat through countless presentations on language acquisition, non-native language acquisition, differences between native and non-native (do they exist, if so, to what extent) etc. I have also seen many language teachers and learners muse on these topics... still one of the most resoundingly sound and insightful musings on this I have ever come across is that of Sir Peter Ustinov.