Poison is a part found in the Cell Stage. It can be unlocked by killing either a Squirty or Puffish, or by being looted from a Meteor Shards. The poison part will automatically spray a harmful poison around your cell. This poison will drain other cell's health, and also renders your own cell immune to other cells with the same part. Likewise, the poison will not be able to harm Puffish or Squirty.
In the creature stage, the part gives your creature level 1 Spit.