It was rumored that zhu zhu pets had lead and other toxic metals in them. They have not been recalled yet and as far as I know they are still under investigation.

http://www.walletpop.com/blog/2009/12/06/will-zhu-zhu-pets-be-recalled-for-lead-or-is-this-just-a-web-my/

http://www.csmonitor.com/Money/new-economy/2009/1206/could-a-consumer-groups-report-lead-to-a-zhu-zhu-pet-recall

http://www.thisisbrandx.com/2009/12/will-zhu-zhu-pets-face-a-product-recall-over-lead-content.html

http://www.tellinitlikeitis.net/2009/12/are-zhu-zhu-hamster-pets-toxic-for-kids-2009-toxic-toy-list.html

There are many other sites with articles about this topic. This is an excerp from the last link I posted:

Dara O’Rourke, co-founder of GoodGuide, tested Zhu Zhu Pets for chemicals with his group, and says Zhu Zhu pets have elevated levels of tin and antimony – a metal with potential health hazards. “If ingested in high enough levels can lead to canced, reproductive health, and other human health hazards”.

Hope this helps.

Wake up Zhu Zhu pets! Zhu Zhu pets go here and there Zhu Zhu pets go every where theres a big world to explor and fun through every door pipsqueak loves the hamster wheel change tueir world its no big deal build it change it rearange it Mr. squiggles in his wheels Zhu zhu pets are so much fun play unitl the day is done you will love your zhu zhu pets cuz tueir so real with out the mess!

I have the song stuck in my head i am dumb to u r not alone