So this is what happened. The Anugypt Strut is a relic containing what was thought to be an ancient example of written music. Zig Zag hummed a section of it, and it turns out it was actually a summoning spell.
Remember the Canterlot Ballet Company performance that Amber Spark got tickets to earlier in the chapter? They adapted the Anugypt Strut into a full ballet and are about to perform it tonight.