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) burning damageItem
Scared Sausage is an in-game item that can be bought from a Shop or can be found in a Crate. Most Items modify the Stats of the player, and some of them provide additional effects.
Scared Sausage
Scared Sausage gives any hit produced by you a 25% chance to inflict burn for 1 + (100%) each second, for 3 seconds. Each additional Scared Sausage increases the chance to inflict burn by another 25%, up to a max of 100% when you have 4.
The Scared Sausage also gives +1 to the base burning damage of weapons that already inflict burning on hit such as the 
Flamethrower. Since Scared Sausage costs more than 1 elemental damage in general, you might not want to buy Scared Sausages unless you actually use its ability to inflict burn. Any Sausage beyond the first also increases the damage dealt by the burn it inflicts itself by +1.
What can Inflict Burn
- Spawned projectiles from
Alien Eyes,
Baby with a Beard, 
Lightning Shiv, 
Cacti Club and other weapons can inflict burn. This used to not be the case, but was changed in patch 1.0.1.3. - Damage from
Baby Elephant, 
Cyberball, or 
Riposte doesn't spread either. - The Explosion from
Bull or 
Landmines can spread fire, same with explosions from 
Rocket Launcher and other weapons can. - The Explosion from items such as
Spicy Sauce or 
Rip and Tear can't spread burn.
Turrets
Engineering turrets (
Turret, 
Laser Turret, 
Explosive Turret, and 
Tyler) can inflict burn via Scared Sausage. Even the explosion can spread fire.
Incendiary Turret inflicts a separate type of burn with blue fire. The damage of the turret can be increased by 1 for each Scared Sausage you have, but it cannot inflict regular burn. Snakes do spread the blue fire of the turret.