In TUI design the selection of metaphors influences user expectations and ease of use. Traditional TUI design processes have not addressed this issue explicitly so far. A reflection of existing approaches for metaphor classification in TUI design helps explaining why TUI metaphors not fitting could mislead users. Based upon these explanations, we gained empirical insight into negative effects caused by selecting metaphors not fitting the situation of use. The paper closes with an outlook on a metaphor-aware TUI specification process founded in both, the conceptual work and the empirical results presented in this paper.