Weed

Putting skeletons to rest for a moment, the school grounds are also infested with these lovable stripey plants, each with a giggling mouth, who seem to love causing mischief and can, under some circumstances, grow into monstrous tree-sized versions. There's an episode where one of them gets jammed in Inky's bottle and keeps feeding on his ink-being, growing larger and more hostile until actually sucked dry by a bunch of Juno's plant sprouts.