In the sidequest "Buying ink" Domastir the writer needs ink. He asks for you to buy some in the itemshop and he gives you 8 Pix to use.
But Grace in the itemshop had already sold the last bit of ink to Padamus next door. To make him give you the ink you must answer a riddle.
"Life it devours, forest, grass or flowers. But it can not be, without human hands. It's useful you see, but help it demands."
-Fire. (Answer in older versions - V 2.5 or lower - was 'Light')
You get the ink if you answer correctly. Talk to Domastir again to receive a reward of 10 Pix and you get to keep the 8 he gave you initially.