D. Law and R. Dilatancy, could explain this long-standing puzzle: why we can run on cornstarch. The authors thank the technical staff of IUSTI and IRPHE for their help in designing the experimental set-up. We also thank Emil Dohlen and students from Polytech'Marseille for preliminary results, This work was supported by the French National Research Agency (ANR) through the Program No. ANR-11-JS09-005-01 and by the Labex MEC

*. Forterre@univ?amu, fr ? Present address

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