Children’s Hospital Boston, whether you’re there for your own kid or not, always makes for an emotional visit. Miracles performed and dreams dashed, all under the same roof. So Children’s goes to great lengths to fill its corridors with laughter. And this brings us to the beloved Bippity Boppity Balls. The Bippity Bop, as it’s known, is an “audiokinetic” sculpture that has elicited awe and wonder in the lobby ever since artist George Rhoads built it for Children’s in 1997. It’s a Rube Goldberg-like contraption in which small rubber balls zip along a multicolored track, triggering a series of sounds as they meet wooden blocks, bells, and metal chambers. The balls whirr as they race, clang as they strike chimes, and go splat as they bounce off platforms. Often you’ll see kids’ faces pressed against the Plexiglas, eyes wide as they track balls around the maze. Part of the allure, I think, is its mechanical precision, in a place, however advanced, that’s still trying to unravel the many mysteries of the human body.