@article{farkas2002social,
  title={Social behaviour: Mexican waves in an excitable medium},
  author={Farkas, Ill{\'e}s and Helbing, Dirk and Vicsek, Tam{\'a}s},
  journal={Nature},
  volume={419},
  number={6903},
  pages={131--132},
  year={2002},
  publisher={Nature Publishing Group}
}