*Can Be Missed*
This is only done on the Police Station level. After you have dropped its health down midway, you will be sent through the ground into the subway station. A subway will pass by every few seconds. To get this work best make the Panda Bear chase you into the subway tracks. Start bringing its health down until the point where it falls to the ground and hope for a subway to pass by on the tracks while hes down.
Note: If you miss this on the first play through, you can replay the Police Station again or start a New Game+. The Police Station is the only place to do this in.