So not only can you play as birds, dogs and cats but you can also play as a shark its so cool guy to see the amount of detail Rockstar Games put into the ocean of gta 5 its amazing and to be able to play as a shark in the ocean and attack people its even better.

Here is a video to help you get it

If you want want to watch the video here is a picture and text tutorials

So to be able to do this you need to get a Peyote

It can be found here

Jump off the back of the pier and dive under the water