This quote is interesting because it's a great example of Snape's irrational anger, as it pertains to Harry Potter. He lashes out at Harry, first, for his seeming impertinence--using Snape's own spells against him--and then reveals that he is the Half-Blood Prince. He knows that Harry didn't already know he is the Half-Blood Prince, thus the creator of those spells. But, irrationally, he chooses to attack Harry for his audacity, even though Harry is clearly operating on manic instinct alone.
This quote is interesting because it's a great example of Snape's irrational anger, as it pertains to Harry Potter. He lashes out at Harry, first, for his seeming impertinence--using Snape's own spells against him--and then reveals that he is the Half-Blood Prince. He knows that Harry didn't already know he is the Half-Blood Prince, thus the creator of those spells. But, irrationally, he chooses to attack Harry for his audacity, even though Harry is clearly operating on manic instinct alone.
--AK