League of Legends (LoL) Question: Katarina item start :?

Thanks.

Use it to counterward if you see your enemy chuck down a ward somewhere. This way you get 25 gold, they lose 75g, and you now know for sure they have no ward there, which lets your jungler camp in a side bush and know that the enemy has no vision of him.

Alternatively just throw it down when Akali shrouds or something.

Thanks! But i still have a question, where to put vision ward? Jungle, river or side-bushes?