A list of all facial muscle movements mentioned in the chimpFACS manual [5] and considered in our present study.

We include the raw count and proportion of facial muscle movements identified in previous studies (i.e., our “observed” configuration list), as well as the raw count and proportion of facial muscle movements that were in our “unobserved” configuration list (identified using our combinatorial model). The proportion of "observed" facial muscle movements was calculated by dividing the number of instances that each facial muscle movement was observed (in column 3) by the total number of facial configurations in our "observed" list (N = 57). The proportion of “unobserved” facial muscle movements was calculated by dividing the number of instances that each facial muscle was generated by our Python model (in column 5) by the total number of facial configurations in our “unobserved” list (N = 238,022). The last column displays the difference in proportion between observed and unobserved facial muscle movements (by subtracting column 4 from column 6).