chlorine dioxide: an explosive gas (ClO2) used chiefly in bleaching paper or starch or soap or flour and in water purification
dioxide: an oxide containing two atoms of oxygen in the molecule
sternocleidomastoid: one of two thick muscles running from the sternum and clavicle to the mastoid and occipital bone; turns head obliquely to the opposite side; when acting together they flex the neck and extend the head