CARNIVAL is also transvestitism, appearing in different clothes, different personality. No exception in Venice. Men in women's clothing, usually. The most vulgar as a joke, the better the tease for everybody.
At times the Gnagas were going around the city carrying with them young babies, or accompanying with other men dressed as infants, to make the tease even more exaggerated.
The name Gnaga seems to have derived from "gnao", the meowing of the cat, because of the falsetto voice exaggerated to make the tease more obvious.