A cat in a factory is tasked with the job of putting a bun on meat. Repeatedly.
As you while away your day, in the cat-run factory where they produce hamburgers en masse, your impossibly dull task is to put the tops on the burgers. Over. And Over. Again.
The idea is that this factory produces one thing and one thing only. Hamburgers. The first drone drags the buns onto the conveyer, the second adds meat and the third - you - puts the tops on the burgers. It's vitally important that you make sure of two things: One, that you don't let a burger go without a top and Two, that you don't put a bun top directly atop another bun. Else you get fired (at least that's what I think happens when you expand over twice your girth).
You see, you are being watched vigilantly by the head cat. If you let your guard up for just a second, you're going to head into trouble. Of course, you take the wrap for the worker next to you who routinely screws up by forgetting to put the patty on the bun. If he sends a naked bun, you reject it by hitting the right click. When the meat filled burger comes your way, hit left click to bun it up.
In case you didn't assume so, there is really little to this game. Click either button depending on what's in front of you. Press the wrong button or no button and you fail. If you can stomach the incredible repetitiveness, this might last you a whole coffee-break. The speed which eventually builds turns this into a blur about half-way through and high scores are more about endurance than skill.