Snape went stiff as a scarecrow with shock as Marlene not only hugged him but actually kissed him! The round eyes and beaky nose only increased his resemblance to a startled owl.
His first impulse was of course to Incendio the blasted decorations, but the damage had already been done. So he exerted himself only subtly: the glitter that landed on him slid off, like water from the back of a greasy duck.