Sow: a pig, a female pig
Sow a field with wheat or rye
Saw: a tool to cut up wood
Soar: a rapid way to fly
Sew: a needle pulling thread
Sore: what makes a man go 'ow'
So: this follows what I said
Which will bring us back to sow-ow-ow-ow
Every language has its own insanities. The worst of English have to do with spelling and pronunciation, the product of hundreds of years of vowel-shifting and freely importing words from languages with different, basically incompatible spelling system, often - but not always - keeping their spelling and at least some aspects of their pronunciation. Hence there is often no way to know how to pronounce a word if you haven't heard it - a novice reader would be entirely unable to guess how many homophones there are in this song, for example.
The whole thing is made much harder by the fact English just has so many more vowel sounds than the likes of Spanish - Simeon Potter's Our Language (1950) counts twelve flat vowels and nine diphthongs, a plausible figure although the sounds are certainly sliced differently in my speech, sixty years on, and in other tables of English phonetics that I have found.
As with many languages, the problem is further complicated by regional variations - all English speakers will probably agree that 'soar' and 'sore' sound the same, but only a few million from the north of England will pronounce 'sew' and 'so' (which are also homophones) anywhere near the same as those. Speakers of rhotic accents - including the Irish, Welsh, Scots, West Country English and most North Americans, especially those living outside of New England and The South of the USA - will pronounce 'saw' differently from 'soar'. Many but not all of those with non-rhotic accents will insert a linking 'r' sound into the gap between 'saw' and 'a'; the more pedantic will not put an 'r' there, but will put one between 'soar' and 'a'; people from the south of the USA usually won't add one in either case. The upshot is that there may be two, three or four quite different sounds between 'sow' (in the sense of a pig), 'so', 'saw' and 'soar'. In case that's not enough confusion for you, some accents pronounce 'horse' and 'hoarse' differently even though 'sore' and 'soar' would be the same.
As mad as English spelling is when considered in relation to pronunciation, schemes to reform it have always floundered, and few believe they will ever take hold. Part of the trouble is that in many cases the spelling is helpful for understanding the language, even when it is unhelpful for suggesting pronunciation - it might make for greater consistency, but we probably wouldn't want a language where 'nation' has a completely different first vowel from 'national', or 'cats' is pluralised differently from 'dogz'. Another problem, of course, is that English is now spoken so widely - reforms that would make perfect sense for North Americans would often fail when applied in Britain, India or internationally, and the upshot is almost guaranteed to be yet more bafflement.
With apologies to Rodgers and Hammerstein for the song, and to everybody who has ever had to learn how to read English. Thanks to all at Gorozika, especially whoever suggested 'Sow, a pig' in the first place.