Snape loses points for Gryffindor and Umbridge inspects his class

During Potions class, Professor Snape removes points from Gryffindor after noticing Harry and Ron restraining Neville. Umbridge, sitting in on the class, begins questioning Snape about his background and why he has never been appointed to the Defense Against the Dark Arts position. Snape responds curtly, clearly frustrated, while Harry struggles with his potion, ultimately failing to brew it correctly.