When using Santoryu (Three Swords style), Zoro holds a sword in his mouth. How is he able to speak normally, without the sword falling?
The official explanation given by the author, Oda Eiichiro, in his SBS1 column, is that it is Zoro's heart speaking. This may not sound any more convincing than Artistic License, but One Piece regularly relies on such unusual logic, so it is not entirely out of place.
1 SBS (Shitsumon wo Boshū Suru, roughly meaning "I'm Taking Questions") is a Q&A column in which Eiichiro Oda answers questions sent in by his fans.
I hate how people always ask this question... Okay, put a pen in your mouth, try speaking You will be able to speak, despite the pen being in your mouth. Sure, your voice sounds muffled, but Zoro's voice is also muffled when he speaks with a sword in his mouth You don't need to move your teeth in order to talk, just your tongue, which I'm pretty sure isn't wrapped around Zoro's sword. I hope I answered your question.