When analysing the functions of wow! I came across sentences likeI repliedWow. Calm down.Wow. Take it easy.
I'm not a native speaker of English but I'm fairly sure that wow! is pronounced differently in these cases (rhyming with American go); it does not sound like a British English diphthong.
The dictionaries I checked only provide the usual pronunciation (rhyming with "cow"). I was wondering if they might be homographs, the "normal" wow! expressing admiration, etc. and the other one apprehension or something along these lines. However, no wow! with this function is listed in any of the dictionaries I consulted.
The interjection meaning “slow down!” and rhyming with (British or American) go is normally spelt “whoa!”.
Perhaps these are just spelling mistakes.
I wonder if there is anything more to it than that.
I’m not aware that the slow-down interjection whoa! is pronounced with something that “does not sound like a BrE diphthong”. As far as I know, it is straightforwardly a homophone of woe, pronounced with the local GOAT vowel whatever it may be.
Other languages seem to use quite different interjections in this sense: French holà!, German brr!, Spanish ¡so!
As a child I learnt a nursery rhyme
If I had a donkey that wouldn’t go(That’s the version I know. The internet offers a rival nursery rhyme that goes “…I'd put him in the barn and give him some corn, The best little donkey that ever was born!”)
would I beat him? Oh dear, no.
I’d say “Gee up, Neddy! Whoa!”
The OED gives spellings and definitions that seem exactly right.
whoa wəʊ ‘a word of command to a horse or other draught-animal to stop or stand still’ (from 1843)
wow waʊ ‘now chiefly expressing astonishment or admiration’ (from 1892)
On the other hand the on-line Urban Dictionary offers further, alternative, definitions of whoa that make it a partial synonym of wow:
1. To express surprise (interj)
2. To express astonishment (interj)
So perhaps there are two possible ways of interpreting this cartoon.