"Ablaut reduplication" explained


I can't find the original, so* I'll embed this screencap of a ?newspaper article for a quick summary.  More details are available in the Wikipedia article on apophony.  Via the discussion thread at the Interestingasfuck subreddit.
"It's a terrible thing to teach language learners, they'll try to agonizingly remember and apply a rule that is complete and totally instinctive even for natives. Same goes for most grammar "rules", which imho are not rules handed down by grammarians so much as patterns they have noticed."
*A tip of the blogging cap to an anonymous reader and to Paul Parkinson, whose comments led me to the source in a BBC Culture column.  And the book from which the cited text was excerpted is "The Elements of Eloquence: How to Turn the Perfect English Phrase," which I've requested from our library.