The plot of the Menaechmi revolves around a pair of identical fraternal twins, who until the end of the play are unaware of each other’s presence in the same town. A series of misunderstandings ensue when the twins are constantly mistaken for each other. The central theme of the play is that of optical illusion as a result of identical appearances, and the inevitable chain-production of errors. The present paper discusses the many layers behind Plautus’ decision to introduce the first in this series of errors in the only episode that features the secondary character of the cook Cylindrus. I argue that the significance of Cylindrus’ part in the play is not to be discovered through a study of his performance, but through the origin of his name and its relation to the core theme of the play: the double, and the recycling of illusion as a result. This is achieved through allusion to the mathematicians Maenechmus, and the latter’s theory of circular proof, which provides a perfect description for the situation at the Menaechmi, of the non-repetitive plot through the recurrence of the same type of error.