Instruct: Classify Amazon reviews into positive or negative sentiment
Query: nasty film with regular use

After using this mug for several months, I began noticing that my coffee wasn't flowing through the sip-hole easily and I wondered what was wrong. I tried to clean the lid and, as noted by the previous poster, found that only a Q-Tip could help me get to the gunk that was trapped in the lid.And, this is not just a little gunk. I cleaned for at least half an hour and was still getting nasty congeled crud out of the lid. Even so, I don't believe it is fully clean. I really hope that OXO re-designs this mug to make it easy to clean because I am usually a big fan of their products. But now, I'm too grossed out. I need to buy a different mug.