I'm puzzled trying to determine how I can 'grab' a tool to clear a square. By default we all get 3 shovels. When I poke at it on mobile, there is no indication that it becomes active before I try to poke the slightly exposed square/tile. I've done enough daily quests in the event to buy a set of tools (including the other two types). Is my assumption of poking a tool then poking a tile correct, or should I be doing something else to enable a tool?