See that little L-shaped thing up there? That’s Apple’s “Dent Inspection Tool.” It’s used to tell Apple repair technicians if your warranty is void.
The technician uses the tool by placing it on the surface of your MacBook. Somehow, they use it to find dents in the casing. There is a small, 1mm spike on one side of the tool. If any part of the tool lays flat on the laptop, it means there is a dent, and that there is possible external damage to the casing, meaning it was possibly caused by a drop or some other misuse by the owner. They do the same with the sides and the corners. The tool must align according to Apple’s guidelines in order for the laptop to be under warranty. If they detect any sort of physical damage, they can say it’s void.
Remember folks, if your MacBook is even a bit dented, it looks like Apple will find out. Bummer. Just try not to drop it, and you should be okay.