Poison Spit states the following:
When you deal damage to monsters give them a poison counter. Monsters take 1 damage for each poison counter they have at the end of their turn. You can get rid of a poison counter with a [Heart] (that [Heart] doesn't heal a damage also).
What happens with counters that are healed? Are they removed from the game or are they returned to the owner of the card? The card seems overpowered in the second case, as it only costs 4 energy. (The same question for Shrink Ray)