Zen Ghosts is a Halloween-night book, and as such the color palette is darker than Zen Shorts or Zen Ties, lovely deep blues and inky blacks and purple-greys, though there's also autumnal red and yellow and orange, with occasional flashes of grass-green. Stillwater the panda, already dressed as a ghost, visits his neighbors just before Halloween to tell them to meet up with him after trick-or-treating because he knows someone who will tell them a ghost story. Addy, Karl, and Michael comply, and are surprised to see that the storyteller is a panda who looks just like Stillwater. The story itself, which comes from a Buddhist koan, is about duality: if we have two selves, which is the true one? Can you even say we have more than one self, or is it just one self? If it's just one, why do we act different in different social circles/contexts? This being a koan, the story doesn't give an answer: you just have to turn it over in your mind. As in Zen Shorts, Muth uses a mix of watercolors and ink for the art in this book, and the combination works really well— I especially love the richness of the watercolors. The text of this book, since it's a ghost story, is mostly pretty solemn, but it's not without its funny/sweet moments, like Karl saving a bamboo-flavored candy bar for Stillwater. I also love that when Michael can't decide whether to be an owl or a pirate for Halloween, Stillwater suggests that could be an Owl-Pirate, which horrifies Karl, who says Michael has to choose to be one or the other. (More duality! And I love that Michael takes Stillwater's suggestion.)