Pea

Peas are projectiles that are shot by Peashooters, Snow Peas, Repeaters, Threepeaters, Split Peas and Gatling Peas. The pea is the basic projectile in the game.

Wikipedia:
A Pea is most commonly the small spherical seed or the seed-pod of the legume Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a (pea) flower. However, peas are considered to be a vegetable in cooking. The name is also used to describe other edible seeds from the Fabaceae such as the pigeon pea (Cajanus cajan), the cowpea (Vigna unguiculata), and the seeds from several species of Lathyrus.

Pea
A normal pea can only be shot by Peashooters, Repeaters, Threepeaters, Split Peas & Gatling Peas. Each of it does 1 normal damage shot to zombies.

Frozen Pea
A frozen pea can only be shot by Snow Peas. Each of it does 1 normal damage shot to zombies, it will also slow down zombies. Slowing effect can be removed by flaming peas, Jalapenos, Cherry Bombs & other explosives.

Flaming Pea
Flaming peas are normal peas that passed trough a Torchwood. Each of it does 2 normal damage shots to zombies with a splash effect which does 1 nomal damage shot to zombies. A flaming pea can remove slowing effects by frozen peas.

Trivia

 * The pea is incredibly big as the head of a zombie.
 * It is unknown where pea-shooters stores the peas they shoot that are bigger than their head.
 * Peas are Bigger than their Real life Real-Life counterparts.