I would say "quite simple!" but it wasn't
I bought a syringe from my local pharmacy (without the needle bit), pulled the plunger bit out and put some tape over the small end (to stop the smoke from escaping while I was filling it with smoke). Then I lit up some incense and held the syringe over the incense until it filled up. I then gently put the plunger back, removed the tape, posed and took the photo while gently pushing the syringe out. The lighting was done by an off-camera flash with an orange filter held over it. Surprisingly, it took only 50 photos to get this shot. Normally I would have expected double or even triple that amount ;D
And as my wife pointed out, the smoke looks like half a skull. Quite coincidental, for sure!
Thanks for the question