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In order to procure the necessary raw materials for knife production, one of us (M.I.E.) went on a diet with high protein and fatty acids, which is consistent with an arctic diet, for eight days (Binford, 2012; Fumagalli et al., 2015) (Table S1). The Inuit do not only eat meat from maritime and terrestrial animals (Arendt, 2010; Zutter, 2009), and there were three instances during the eight-day diet that M.I.E. ate fruit, vegetables, or carbohydrates (Table S1).

Raw material collection did not begin until day four, and then proceeded regularly for the next five days (Table S1). Fecal samples were formed into knives using ceramic molds, “knife molds” (Figs. S1–S2), or molded by hand, “hand-shaped knives” (Fig. S3). All fecal samples were stored at −20 °C until the experiments began.

We procured pig hide, muscle, and tendons, and these were also stored at −20 °C until two days before the experiments began, at which point we allowed them to begin thawing at 4 °C. Minutes prior to the experiment, both the “knife mold” samples and the “hand-shaped knives” were removed from the laboratory freezer and further sharpened with a metal file (Fig. S4). The knives were then buried for several minutes in −50 °C dry ice to ensure they were sufficiently frozen before any attempt at slicing. The study was approved by the Institutional Biosafety Committee at Kent State University.

We began our cutting experiments with the hide, reasoning that if our knives could not cut hide, then subsequent attempts with muscle and tendons would be futile.

Neither the “knife mold” samples, nor the “hand-shaped knives” could cut through hide (Figs. S5–S6). Despite the hide being cold from refrigeration, instead of slicing through it the knife-edge simply melted upon contact, leaving streaks of fecal matter (Fig. S4).