The phrase λεγόντοιν represents a rare and specific morphological form: the dual optative of λέγω (λέγοιτοιν) used as a passive participle (or potentially a contracted form of λέγοιτοιν in a periphrastic construction), which is highly irregular for Aristophanes. While the dual optative exists, its usage here with the infinitive γνῶναι to express a prohibitive or potential nuance ('lest they be understood to speak thin things') is syntactically complex and likely involves a dialectal or poetic contraction not found in Attic prose. This construction is not merely an intermediate grammatical exercise but a deliberate archaism or metrical adjustment that challenges standard parsing of the dual optative in a comedic context.