It is a gua sha.

I bought it when it first became popular and used it for facial massages, but I saw on YouTube that using it incorrectly can actually cause the skin to sag, so I got scared and put it away.

I recently watched a video about gua sha and heard it's good for relieving thigh swelling, so I rubbed my thighs really hard, and now I have huge bruises.

Please do not rub your body too hard like I do when doing gua sha.