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Remember the Subsurfaces from the last step ? And remember that the snake had always the same grinning facial expression ? Now, let's make some animated sprites1) - not pygame sprites, but surfaces that show different images of an animation cycle, like a bird flapping it wings.
Instead of painting all the single pictures of an animation cycle myself i prefer to use ready-made sprite sheets. In the data folder, you will find a spritesheet2) from http://www.flyingyogi.com showing several pictures of an animal.
With the help of pygame's subsurface command, i will show you how to extract single images from the sprite sheet and use them.