Bob Godfrey (1921-2013) was a celebrated British animator behind the cartoons Roobarb, Noah and Nelly in… SkylArk, and Henry's Cat. But it's his 1984 TV commercial for the chocolate bar Trio that I really dig.
From a 2009 interview with Godfrey in Vertigo:
MP: So in the 80's as well as doing Henry's Cat you were still doing advertisements and I remember your 'Trio' advert. I remember the little girl…
BG: That was taken from one of our films that they'd seen of this little girl who liked imitating foghorns! And they saw this and they thought it was great! It was just so funny that a little girl would open her mouth like that and do a great sound but it did come from one of our things, I can't remember now what it was. It was a little girl – her hobby was imitating foghorns! Probably a Stan Hayward idea, very good.