[r9etb]

On page 747 we read, “...and Phineas Nigellus called, in his high reedy voice, ‘And let it be noted that Slytherin House played its part! Let our contribution not be forgotten!’” But I’ll be doggone if I know what he’s talking about!

Slughorn was fighting in his pajamas, for one thing -- he came puffing up the stairs on Charlie Weasley's heels. He probably had a few Slytherins who decided to stay with him.

[Hoodlum91]

I took it to mean Snape’s role - he was a Slytherin.