8 groom by hand grin-full-closed Goodall Full closed grin: Both upper and lower teeth are revealed by the horizontal retraction of upper and lower lips, and the teeth are closed, or almost closed. Plooijs Grin-full-closed. Kanos Grin for bonobos of Wamba. See video. grin-full-open Goodall Full open grin: Both upper and lower teeth are revealed by horizontal retraction of upper and lower lips, and the teeth are partially or widely open. Plooijs Grin-full-open. Grin for bonobos at Wamba. See video. G grin-low-closed Goodall Low closed grin: Only the lower teeth are revealed, and the teeth are closed, or almost closed. Absent in bonobos?. See video. grin-low-open Goodall Low open grin: Only the lower teeth are revealed, and the teeth are partially or widely open. Absent in bonobos? 3.