Daemonica

I am really crazy about this game, but also this game is driving me crazy so I need a little help, in the chapter four after doctors dead, I have a New quest and in this quest I must Found a stone, but the only clue that I have its a poem, and I dont understen...

When the guard is thirsty i cant find the mayor.

I cannot figure out how to get the herbs out of inventory. I also have no idea how to make people speak to others except for the dialogue which originally comes with them. Any help would be greatly appreciated. Thanks.