I've noticed that most people keep their food and drinks in containers. Basically, it's near impossible to poison their food/drink, so this skill is quite useless at low ranks (though I do have some inkling how this skills can be very powerful at higher ranks). For now, a poison thief needs a plant to be effective in 'tricking' a person to eat the food. For myself, if I find a berry pie not in my knapsack, I'll be dropping and destroying it.

Anyway, my suggestions is this for the poison path :
1. Keep poison food, poison drink as the same skill. The skill should be poison food/drink.
2. Have a new poison skill as poison/contaminate air. By applying this skill, there is a chance that edible foodstuff/drinks (even within bags and containers) can be poisoned through the poisonous gases that attack them. The number of poisoned items increases with levels and randomly. This makes the poison thief more effective on lower levels and feared at higher levels.

Comments.