관계대명사 who와 distended 쓰임이 궁금해요

두 문장이 헷갈려서 질문드려요.
1. “A friend of mine had an overweight Labrador retriever who needed to be put on a strict diet for health reasons.” 선행사가 retriever인데 왜 which가 아니라 who인가요?
2. “There was your dog up on the table, licking its chops, stomach distended.” 여기서 distended가 과거분사 형태인 이유가 궁금해요.
친절한 설명 부탁드려요 ㅠㅠ