Musical Mysteriousness

Last night, the guys and I sat together in the living room. Bob and I were in the big chair, watching this awesome band on the computer. Mr. Rosenberg and Teddy sat on the couch.

We all heard it.

Mr. Rosenberg's ukulele that lives on top of the piano, made a sound. It sounded as if someone had plucked one of the strings. No one had touched the ukulele in at least a week. Nothing had fallen on it and yet, it did make a sound.

We all heard it, but none of us could explain it.

Can you?