My deer friend with his nose up smelling the air for female hormones. At times they will be so much into the rut they will go without eating if a females hormones are in the air. The musk gland is near their eye and will open and close as they breath. It’s more noticeable on the mule deer then the black tail deer like this one. The deer aren’t alarmed seeing me so then get rather close. This is a view from my porch or from the front door window. The views are always amazing.