The following sequence of photos shows the collision between two P-51s on landing at OshKosh.
(Thanks to Ted Brindle for providing the photos)

The first set of photos shows the lead aircraft touching down prior to the following aircraft.
As I understand it, the trailing aircraft should normally touch down first, as it will slow down more quickly than the aircraft still in the air.

The trailing aircraft, which I'm guessing can't see the lead, makes contact with the lead and tries to pull up.

The trailing aircraft impacts the ground inverted as the lead aircraft slides down the runway on it's nose.

If you look closely, you can see the damage to the lead aircraft.  The port stabilizer is gone and there is a gash in the port side of the fuselage from a prop strike.

What a waste...  I understand that the trailing aircraft was a very rare, newly-restored, P-51A (or maybe B).