Ending "-yo" makes a sentence polite a bit and informal. (it's kind of "해요체-Haeyoche") 1.아니(a-ni) - impolite and informal 2.아니요(a-ni-yo) - polite and informal 3.아뇨(a-nyo) = a contraction of "아니요" As for "가위-바위-보", /w/ sounds as in "가위", "바위" should be prounounced exactly but when we are saying it fast, often the /w/ sounds are ignored because /이/ sound is easier to pronounce than /우/ sound. This happens in conversation. ^________^