What do they do? I think there meant to do something, because they look rare, or are they just food?

You can feed them to your pets. They use to be really cheap, but now there's an achievement that you can get if you feed one of your pets 25 of them. Naturally they've gone up in price because of this.

oh okay thax I'll probably sell :3 since there aren't much in stock

People have them in shops all over. They're an unsearchable item, though. That's why you think it's not in stock, I'm assuming?

You have one too?? I searched them in the shops and it never shows up.. regardless the fact I know i haveone for sale in my shop.. it is strange. O.o