Wasn't sure if this has been shared yet. it was in the official guide too, I think.

When you are at the Galbadian Missile Base, you are trying to use a computer terminal to (re)configure missiles. On this terminal, there is an option to view the various equipment involved in the missile strike. By holding down [Triangle] and [Square] press up or down (try both). You'll get hidden views of a Soldier and an Elite Soldier and they dance on the monitor.