I'd never do it, shouldn't I have searched for hours...

Ok, I'm completely dizzy.

I've searched through the archives and I haven't been able to find it. What am I searching for? I'm searching for the tutorial that explained how to achieve a kind of moving smoke... well, I don't know if I'm explaining myself, but I can remember that there were two tutorials explaining how to do it, one featured a character from an anime with a gun, and smoke going out from it. Does it ring a bell?

'Cos I haven't found it.

:(

Thanks in advance if any of you remembers and tells me!!

Edit: Three fast and wonderful users have already helped me!! Thanks!!