This paper investigates the synaesthetic constructions in Persian with the aim of finding out what motivates them despite their incongruous syntactic-semantic assignments. It is argued that these paradoxical elements require a metaphoric/metonymic frame to assign appropriate lexical units (LUs) to their corresponding syntactic categories (NP + rɑ +VP and NP + AP). The discrepancy derives from the semantic aspects for which frame semantics provides two types of explanations: internal and external frame factors. Internal factors deal with the metaphoric/metonymic compatibility or similarity between frames, while external factors underline the use of lexical items from one subframe to fill the vocabulary gap of a different subframe. The argument is that this gap owes much to the indirect contact between the Phenomenon (e.g., an odorous substance) and the Body-part (e.g., nose) that perceives it. In short, the analysis of our data reveals that synaesthesia is not only an economical strategy for modifying the senses, but also a natural mental strategy for interpreting vague experiences. A configuration of the incongruent construction of ‘smell’ and ‘hearing’ will be proposed to generalize such an analysis.