Re: the reference to yo-yo's...
During the early-mid twentieth century, some glow-in-the-dark things such as toys and watch and clock faces were painted with what turned out to be a dangerous radioactive substance. I'm not a physicist so don't hold me to it, but I want to say it was radium. Maybe J R or some one can clarify that point (I'll check into it too). So it's possible that the reference there is to a glow-in-the-dark yo-yo.
There's also the possible symbolic reference to dangerous feelings that the main character feels the need to keep hidden.
Re: the reference to yo-yo's... During the early-mid twentieth century, some glow-in-the-dark things such as toys and watch and clock faces were painted with what turned out to be a dangerous radioactive substance. I'm not a physicist so don't hold me to it, but I want to say it was radium. Maybe J R or some one can clarify that point (I'll check into it too). So it's possible that the reference there is to a glow-in-the-dark yo-yo. There's also the possible symbolic reference to dangerous feelings that the main character feels the need to keep hidden.