Not sure if they're known outside of Belgium/Netherlands/France. They're a candy made in Antwerp originally (now in the Netherlands).

Very sour hard candy, lemon flavored. With a lemon powder center. So when you get through the candy layer, all the extremely sour powder is

released and you go Eep.

Eep! I live in the US, never heard of them, but we do have things similar. That's TOO sour, you can have mine!

That sounds nice. I'd love to go Eep!