The show practically invites us to chuckle at the neatly interlocked way that a song like "Honey, Honey" or "Knowing Me, Knowing You" will dovetail with the (thin) motivation for singing it. And that’s why the dithery sweet mindlessness of "Mamma Mia!" is part of its magic. The show serves as a friendly frame for the songs without threatening to get in the way of them.