Annihilative fractals of coffee on milk formed by Rayleigh-Taylor   instability
  We have discovered a new fractal pattern, coffee exhibits on a horizontal surface, with a fractal dimension $1.88 \pm 0.06$, when a heavy coffee droplet interacts with the surface of lighter milk. Parts of coffee pattern on the surface disappear due to Rayleigh-Taylor instability, and the annihilative behavior produces the fractal pattern. Coffee fractals and the Sierpinski carpet have common features, such as the fractal dimension, annihilative behavior, and an exponential decrease of the pattern area. It is suggested the formation of fractal follows a rule similar to that of the Sierpinski carpet. 
Michiko Shimokawa and Shonosuke Ohta