This is a less straightforward application of the "flow noise" technique. Instead of doing a sum of closely spaced octaves, we skip one octave after the first and take a jump with a factor 4 to create a more blotchy pattern on the largest scale with noticeable "hot spots", we don't warp the texture as much, and we warp each term progressively less. We then generate a pattern based partly on the noise value, but primarily on the length of the sum of the gradients for a more "wormy" look. Finally, we apply a fire-like color scheme with a blend from black through orange to yellow.
This is a somewhat "brittle" shader: changing some of its parameters even a little can change the pattern quite a lot, and it took some tweaking to get the look we wanted. We were aiming for a sort of stylized, cartoonish rendition of the turbulent surface of a star. Whether we succeded is of course a matter of opinion. In any case, we think this is a good example to show the great flexibility of animated "flow noise". The method seems to have fallen into oblivion since it was first presented back in in 2001, and that's a shame.
// Fragment shader code goes here