In the HD version of Eversion, the background also changes when eversion occurs. Pronation (eversion) and supination (inversion) occur along the oblique axis of the ankle joint. Pronation of the foot is a compound movement that combines abduction, eversion, and dorsiflexion. The severity of flail leaflet varies, ranging from tip eversion to chordal rupture. Average subtalar motion is 20-30 degrees inversion and 5-10 degrees eversion. It is all completely internal, except for genital protrusion (eversion) during mating. The injury is caused by a combined abduction external rotation from an eversion force. Penis retraction is usually a fast process, although much slower than eversion. In topology, Petit worked with Bernard Morin on the torus and sphere eversion. Eversion (from the verb "evert") is the process of turning inside-out. There can be associated eversion of the eyelids (ectropion). Eversion of the foot occurs at the subtalar joint. An existence proof for crease-free sphere eversion was first created by . The muscle assists in weak plantarflexion and eversion of the foot.