I think you would be able to quickly tell older students that when the music started they needed to trade their cards and then look inside to start the activity, but I think the younger kids didn't quite understand that. I also found that a lot of them needed me to read the activity that was inside the shark, so then they weren't quite as active as they could have been during the instant activity.
The quality was also not up to par. The students didn't understand that when the music wasn't playing they were supposed to do the activity that was written on their shark card. The students also had trouble reading some of the things on their cards or understanding them so I had to explain them to them. To correct this in the future, I would choose activities for the shark cards that were easier for the students to perform and I would have played different music for when the students were supposed to be performing the shark activity.