How to play saxophone. Flutter tongue. This particular effect is somewhat similar in sound to growling.
How to acheive it is not though. Flutter tongue, as the name suggests, involves fluttering the tongue whilst playing.
Start practicing this one without the saxophone. Lads, when you were younger did you run around making pretend machine gun noises with your tongue? Girls, did you try to copy a cat purring? Well the sound you made is what you need to acheive to create flutter tongue. To be fair though, it's not really the sound we are after, only the vibrating of the tongue. This is what makes the flutter tongue effect.
Place your tongue very lightly on the roof or your mouth or close to it. You don't have to touch the roof of your mouth. Now quickly breathe out heavily through your mouth.
Your tongue should have vibrated. Personally I prefer to put the tip of my tongue just so as it's touching the right side of my mouth, just by my teeth. You may want to try that.
Once you've acheived the sound try doing it with the saxophone. Not so easy now is it!
You should get to a point where you will be able to flutter your tongue without using large amounts of air pressure.
Again, this is a practice thing and will only get better with plenty of it.