Left Mouse Button and Right Mouse Button :)
Gotcha! But since my mouse disappears on the game, even though the item glows, I can't see where I'm clicking and nothing seems to happen.
try playing with j and k keys :)
So I did and it worked! Having more clear instructions on the game page or in-game would be great to. And I don't really know what to do in the game, even with the screenshots, and hitting the rocks or trees doesn't show me that anything happens.