Jews are forbidden to eat pork, because according to the Torah, pork is not kosher. The Bible gives two qualifications for what animals can be consumed: any animal that has cloven hooves and chews its cud can be eaten. Pigs don't meet the second qualification, as they don't chew cud.
There are many rules that Jews must keep to in order to follow Jewish dietary laws. Seafood is restricted to anything that has fins and scales, so shellfish is forbidden. Birds of prey and scavengers are forbidden, as Jews are not allowed to eat any animal that has a predatory nature. All fruits and vegetables are permitted, as long as they do not have bugs on them.