Pea

Peas are projectiles that are fired by Peashooters, Snow Peas, Repeaters, Threepeaters, Split Peas and Gatling Peas. The pea is the basic projectile in the game, and therefore a single pea is the base unit for measuring damage.

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 and 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 and other explosives. A frozen pea will become a normal pea after passing through a Torchwood.

Flaming Pea
Flaming peas are normal peas that have passed through a Torchwood. Each flaming pea does the equivalent of two normal damage shots to its target, with a small AoE radius with a damage of 1 normal damage shot. A flaming pea can remove slowing effects by frozen peas peas, or other freezing plants.

Zombies' Peas
Peashooter Zombies and Gatling Pea Zombies (from ZomBotany and ZomBotany 2) fire peas. They hit plants for half the damage of a bite. Plants that are short enough will not be hit by them.

Trivia

 * The pea is incredibly big, slightly bigger than the size of a Zombie's hand.Allpea.png