Whenever someone comments on your hub they are automatically set to follow that hub so when you go back in and reply to their comment they will get a notification. Have you noticed a little number at the top of your page that changes all the time. That is the number of notifications of all the hubs you follow. Click on it and it will show you everything that's going on with the hubs you follow. I always read the replies of the hubs that I've commented on because it is a way for us to communicate back and forth. I hope this helps.
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