Bailey worries Dr. Webber is mommy-tracking her and becomes Derek's intern for the day. George begins a relationship with Callie and finds her living in the hospital. Meredith takes up knitting -- and a vow of celibacy. Cristina competes with the Chief during classroom exercises. Burke tries to teach Alex a lesson about bedside manners, but it's a lesson that falls on deaf ears. Izzie tries to get George to move back into the house. George discovers that Addison's patient is Meredith's half-sister. Meredith meets Doc's vet, and takes a shine to him.