The lower case. Apple's using wide, thin black rubber feet on the Unibody Pros, a departure from the small stubby bumpers on the Aluminum revisions.

There are ten Phillips screws around the perimeter of the lower case to remove:

Seven 3 mm screws

Three 14 mm screws

Apple's user manual for this computer has instructions to remove the lower case. But they got the length of one of the screws wrong. We promise to get them right in our repair guide.

The computer's serial number is engraved in the aluminum lower case, not the upper case like the other Unibody machines.