Many People Are Just Figuring Out The Purpose of Those Doodads On McDonald’s Drink Lids

But what are the rectangle doodads for?

McDonald’s customers are just now discovering what the buttons and ridges on the top of the drink lids are for — and they’re lovin’ it.

A video posted on the “Today Years Old” Twitter account — a reference to the viral phrase “I was today years old when I learned … ” — shows someone pushing the buttons around the straw on the lid of a drink from the fast food chain.

While many people commented that they already knew what the circular nubs are for, many were shocked to learn the purpose of the rectangular ones.

Lots of customers correctly guessed that the circular buttons were indicators of what drink is in the cup. Each button has a label: “diet,” “cola,” “RB” for root beer, and “other.”

But the function of the smaller rectangle buttons next to the circular ones wasn’t as obvious: The ridges are used to correct a mistake if a server presses down the wrong circular button. 

For example, if they accidentally push down the “RB” button instead of the “diet” button, they can click the ridge next to the “RB” circle and reset the lid to correct the mistake.