Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Sand doesn't flow, don't buy it.

I bought this timer for my children to time their piano practice. It does not work at all. When we first received it, the sand flowed but there was always a little bit left at the end, and we had to tap it to make all the sand drip down. Then it stopped working completely after only a week!! The sand was stuck and it did not flow at all. It's a piece of junk, we are throwing it out. Don't buy this product.