Bottle
Hint 1
Follow the coroner’s instructions; add water to the bottle, wait for the watercolor to turn, and then blow through the straw into the bottle.
Can you see the water change color again?
If you don’t, then possibly an ingredient is missing. Read the solution.
Solution
The watercolor should, by blowing through the straw, turn from blue to green.
Now you can conclude that arsenic was found in the teacup of Nicolaas’ teacup.