Wonderful piece of animation!
To me, the animation conveyed the trappings of addiction. It starts out pleasant and comforting, but even near the beginning a hint of malice crosses the smoke's face... The smoker eventually gives in to the lustful pleasures, despite the small warnings, as seen with his initial coughing. He keeps going back to his cigarette, wanting more pleasure, and the smoke keeps giving it to him.
...But after so long, addiction shows its true colors by taking away his health and betraying him. By now it is too late, and addiction has consumed him while he slowly dies.
Ironically, I've found the flash itself addictive! The pacing could've been a bit better, but I'm pretty sure that was due to music synchronization constraints. The flickering black-and-white is distracting for the first viewing or two, but after multiple viewings (unless one is prone to epileptic seizures), it's not quite as noticeable. The graphics are amazing, clean, and beautifully done, especially considering that a lot of it was shape tweening, which is hard to pull off convincingly.
You do some amazing work, and I hope to see more in the future!