User blog comment:I HEART TWILIGHT SAGA/Jasper/@comment-86.142.65.111-20090824122946

Right. I don't know if you've noticed this, but when Bella was bleeding in the ballet studio, Jasper is fully fed, and therefor, not thirsty, and strong enough to resist the scent of her blood.

In New Moon, if you look at posters, Jasper has coal-black eyes, thus meaning he was thirsty, and therefor, not able to control his actions when he smells her blood.

So long story short -- Twilight (Ballet Studio) Jasper = Well fed. New Moon (Cullens house) Jasper = Thirsty.