Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Creates gas rather than reducing it.

I'm so disappointed in this product. All of it ended up in the recycle bin after less than a week.The nipple collapses in upon itself pretty severely, creating gaps between my son's mouth and the nipple, through which he gulps down air. There's no air intake in the nipple so eventually the vacuum is so strong no more milk comes out. The only way to break the vacuum again is to pull the nipple out of his mouth and let it fill out. We have to do this about once a minute while feeding him, so maybe 20 times per feeding! Outrageous.We got these to try and reduce his gassiness, but instead he swallows so much air while feeding, he winds up with lots of gas and can't sleep.