Calm the Zombie Nerves
Play the Piano using Rebecca.
Piano location: Research Facility (2ndF), Bar.
To get to the Piano Bar you require the Water Key. The Key can be found in the Facility Basement Training Room after solving the Puzzle withe the Gates.
Facility Main Hall (2ndF) > Art Room > Piano Bar (Leech Zombie is outside the Bar).
The Story requires you to play the Piano with Billy, but as a joke play it first with Rebecca (WARNING: SHE SUX
)... Achievement Unlocked.
I take no Credit for the Video.
Hope it helps