The Spark Shot is an experimental weapon developed by Umbrella for dealing with unruly B.O.W.s.
The weapon can be obtained by Claire Redfield on a dead body at a dead end the Factory Passage, where the Shotgun Parts should be (found in both Scenario A & B). It is basically a large-sized stun gun with an effective range of 10 feet. It is Claire's counterpart to Leon's flamethrower.
The Spark Shot fires from an unknown power source (likely a battery), and its ammunition count is represented as a percentage (like the SMG). It's initial ammo is 100%, and each shot takes up 5%. It takes up two inventory slots.
This weapon has one good purpose; help Claire defeat the Birkin G-Mutation. Though the weapon is strong against Birkin, it only does average damage against most other enemies, giving it little value beyond this encounter.
As an interesting side note, the Spark Shot can hit enemies on the ground without having to aim down due to its wide spread. No spare ammo can be found for the weapon in the entire game, making it useless once empty.
The weapon was originally known as "Air Taser", according to hacked files found within the game's Trial Edition, and it was supposed to have additional ammo like the submachine gun, but its name was changed and the ammo was removed prior to the final release. Its names were written in Japanese, and are believed to have been placeholders.
In the Comics
In the non-canon Resident Evil Comics Magazine, the Spark Shot is used by Patrick Brady during his cleansing of the Raccoon City Zoo. He carries the weapon slung across his back, employing it against a zombified gorilla named Bubbles, causing the undead simian's eyes to rupture.
The weapon appears to have been some sort of less-than-lethal alternative to conventional weapons employed by the Zoo, although the model Patrick uses may have had multiple settings, or he may have modified it to be effective against zombies.
Mr. Venk uses the weapon to immobilize a G-virus infected Dexter Whitlam.
"High voltage gun to repel experimental animals. It uses Spark Shot rounds and has a range of 10 feet."