I was on youtube and saw secret scenes where funny things happen. One ocelot falls all the way through the plane instead of getting on and another where snake falls off the cliff when parachuting in. How do these happen?

It comes with the package. it's in the secret theater.

When starting a new singleplayer game, the choose I like MG3 and save the file to your memory card, then insert disc 2 and choose secret theater ;) ^_^

either that or just beat the game then you get it