Rita takes a step back, too, unsure of what the hell he could be summoning. Libraries tend not to be great places for that kind of magic... but it turns out that what he summons isn't nearly big enough to be a problem.

"Nigella?" Rita stares in surprise. "You learned magic just to bring back your talking rat?"

Not that anyone really needs a good reason to learn magic. Learning is its own reward! But Rita's about as surprised as Nigella sounds. Didn't she just kind of nag at him most of the time?