-ㄴ걸 states something as a gentle push-back or a small discovery, softer than a flat statement: 좀 출출한걸? 'a bit peckish, actually.' It often trails off with dots or lifts into a questioning mark, inviting the listener to agree. This form attaches to descriptions and to nouns with 이다 (숟가락인걸, 궁금한걸); with action verbs the equivalent is -는걸. All the lines here are casual, without 요.