Why did Snape call Lily a 'Mudblood'?

[Carol]

No: HPFGUIDX 177589

Jen wrote:
> > I've got a question for a slow day: why *did* Snape call Lily a 
Mudblood?  Also, I'm curious how others read Snape's Worst Memory 
given his new memories in DH.  Did the resolution work for you?  I'm 
on the fence about this part.

Mercia responded: 
> He was also a fifteen year old boy deeply and publically humiliated
 by his bitterest rival in front of the girl with whom he was 
obsessed. He knew James fancied Lily. He suspected that she wasn't as
 indifferent to James as she claimed. He couldn't outshine James in 
anything and now the one before whom he would want to appear cool and
clever and skillful has to come to his aid. Of course he is going to 
repudiate her help in the most violent way he can think of. He 
wouldn't even want her to see him in that situation, let alone be the
one to restrain his tormenter. So he hurts the one he loves in 
response to the hurt he feels. Not mature behaviour. But for me very 
believable in such an isolated and tormented boy. It would certainly 
be a bitter memory for him and one he would want to conceal from 
Harry. But surely the memory of Lily's death and his part in it in 
relaying the prophecy to Voldemort must rank as his *worst* memory. 

>
Carol responds:

While I agree that Severus fancied Lily and most of the rest of your
post, I'm not so sure about "couldn't outshine James in anything."
Judging from that detailed response to his DADA exam and Slughorn's
view of him, I'm pretty sure that he excelled in both of those
classes. (No doubt James outshone him in Transfiguration, considering
that he put all that work into becoming an Animagus, but we also see
his brilliance through McGonagall's and Lupin's rose-colored glasses.)
If Sirius Black is to be trusted, Severus came to school knowing more
"curses" (surely, schoolboy hexes) than half the seventh years and we
see from his Potions book that he was brilliant in both spell-creating
and potions improvements.

How much of his brilliance Lily knew is hard to guess. She probably
had a good idea of his proficiency in Potions since, according to
Slughorn, she was a natural at the subject herself. Not a word from
Slughorn on James's abilities in the subject, however.

Lupin suspects that Severus was jealous of James's proficiency as a
Quidditch player, but based on "The Prince's Tale," he was more
jealous of James's status as a celebrity or schoolyard hero, which he
felt was not deserved. He didn't want Lily to like James and was happy
when she called him a "toerag." So rather than saying "he didn't
outshine James at anything," I'd say that James received recognition
for his talents and Severus didn't (except perhaps among his Slytherin
friends). Ironically, Harry and Ron acknowledge the HBP's genius, but
they don't know who he is (and Snape only knows that Harry is using
his book to get marks he doesn't deserve in Potions and using his
spells, not that Harry considered the HBP a genius and a friend).

BTW, if it matters, both Severus and James (also Lily and Remus, I
don't know about Peter and Sirius) were actually sixteen at the time
if the tombstone dates in DH are correct. Kids with January or March
birthdays would be sixteen, not fifteen, by the time the OWLs were
conducted in June.

Carol, who agrees with the rest of the post, particularly as it
relates to Severus's feelings and the reasons for his humiliation