I didn't get the unicorn thing either, but it's explained better in the longer post (https://www.redblobgames.com/x/2635-a-vs-an/ https://www.redblobgames.com/x

I didn't get the unicorn thing either, but it's explained better in the longer post (https://www.redblobgames.com/x/2635-a-vs-an/ https://www.redblobgames.com/x/2635-a-vs-an/). Unicorn is pronounced starting with a sound like 'you', which starts with a consonant.