Hard to resist, in a fowl situation like Carnival, not to tease this community of which Venetians weren't really "so fond of".
Hence the masks with a long nose, shabby clothes and the ever-present Bible in their hand.
The presence of Jews in the territory of the Venice Republic is acknowledged since the year 945 a.d, but until the late 14th century, the Jew population was not so consistent and stabilized.
They mostly were proceeding from the Central Eastern section of Europe, and had as a residence, the "ghetto", which was the area where the waste of the foundry were disposed, from the Italian word "getto (throw away).
Two bridges kept communication between the Ghetto and the rest of Venice, and with sundown their heavy gates were closed, so nobody could go in or out. The Jews were thus segregated, but at the same time protected.
Jews occupation was mainly in lending money for an interest and other similar activities, which were forbidden to Christians by the Church of Rome.
So the Jews presence was highly justified in a city that was doing commerce with half the known world, and with lots of money rolling around.
