For everybody who had a wrong guess and for the anonymous person, I have consolation prizes: another massage device. I have no idea how this thingie is called in English and my dictionary doesn't know either. Literally translated it would be hedgehog ball, which I think is a cute name.
Help yourself:
Edit: meanwhile my own brain started to function again (although I didn't have a brainshower in the meantime
). Suddenly I thought 'massage ball', I bet that's what they're called. And low and behold, a quick google search with that term showed me the expected pictures. Sometimes it's soooo easy!
But now you know what a cute name we Germans have for them
.