and people wonder why we say PHP is a meme

Ah, I understand now. The expression is evaluated like this:

• $a == 1 ? "one" : $a == 2 ? "two" : $a == 3 ? "three" : "other"
• $a == 2 ? "two" : $a == 3 ? "three" : "other"
• "two" ? "three" : "other"
• "three"

If you think PHP is weird, go look up ZZT-OOP, the scripting language from Tim Sweeney's first game.

(No, a scripting language for game characters doesn't need integers. If you need to count, you can do that by moving blocks around on the game board.)