In the last decade, increasing attention has been devoted to exploring some aspects of yawning in non-human animals. With their chin red mark, bony paranasal swellings, male large brains and long canines, drills ( Mandrillus leucophaeus ) offer a robust model for testing hypotheses on the phenomenon. We identified two yawn variants (covered, Y CT and uncovered teeth, Y UCT ) which differ in terms of recruitment of muscular act...