I think Shark Heart says that love, whether for a romantic partner, parent, child, friend, or oneself, is a process just as much as it is an action or feeling. There’s a line at the end of the book about Wren seeing life as “a spiraling trail up a mountain. Each circling lap represents a learning cycle, the same lesson at a slightly higher elevation.” Through Lewis, Joy, and really, all the characters she meets, Wren gets multiple opportunities to climb the mountain of knowing herself. The title, Shark Heart, actually applies to both Wren and Lewis. While Lewis has a literal shark heart by the end of the novel, Wren’s shark heart exists on the metaphorical level. Just as a shark can only swim forward, Wren persists in love, wholly knowing the risks.