Quote from tile on December 9, 2013, 6:06 pm

One day, a turret found a can of something called soda lg. the turret asked glados what it was, and glados simply said: "it's the particle energizing portal stimulation input. i had to rename it because of copyright." the turret then asked glados how she came up with the name. "well, i was going to come up with a good name, but one of my discs reversed."

this is a joke, pun, and a riddle all at once. here's the explanation:

Punchline
[spoiler]soda lg is glados spelled backwards. glados' name appears on one of her discs.the reason glados had to re-name the can is because it's a can of pepsi, as spelled out by the first letters in each word.[/spoiler]