We have a Mozart Cube which was a present from T.'s older cousins to him when he was born. It got a little banged up, but other than needing new batteries, seems to work fine. Tonight, while A. was lying on the sheepie on the floor, I put the cube next to her and pressed one of the buttons. She listened and looked and when it stopped, she rolled onto her side towards it and reached out and pressed one of the buttons. She fiddled with it on and off until she knocked it past where she could reach it, and then she complained until I put her and it back on the sheepie, which they'd migrated off of (it completely, her mostly).
I then called her grandmother and told her she'd better come for a visit soon because A. is apparently growing up very quickly.