Pasunmotdeplus is a mute because Brutus cut out his tongue. Yet in the scene where it first looks like he's singing 'O solo mio', you can clearly see his tongue.
While it is stated (and shown) near the end that whoever used the tainted magic potion has a blue tongue, a few minutes earlier when Brutus has already drank the potion, his mouth is wide open when he is holding on to the reins and his tongue is clearly visible for a while. It is not blue though.
Speaking of Brutus, Cesar mentions the seven plagues of Egypt. There were ten plagues.