While fucking your guy or girl from behind, you hoot like an owl. When they turn back to see what is happening, you clinch their head and spin it around (180 degrees like an owl), and you shove your cock in his or her mouth.
Steve is fucking Jill from behind. Steve says, "HOOT, HOOT"! Jill says, "What is that noise? Steve grabs her head and twists her head 180 degrees and shoves his cock in her mouth. While continuing to HOOT like an owl...thus an Owl Clinch.