-(으)ㄹ 듯 말 듯 pairs 'seems it will' with 'seems it won't', landing right on the edge between them. Every line here is that frame: 기억날 듯 말 듯한 굴라쉬 (goulash he can almost but not quite place), 딸기 향이 약간 날 듯 말 듯 나요 (the strawberry scent is barely there), 잡힐 듯 말 듯 (forever just out of reach). It always means on the verge, never actually one or the other.