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I ran out of time on this one and my last sentence got cut off. Eventually I'll redo this as two separate videos. But for now, I'll just explain here in case someone wants to know:
I was just saying at the end that if you are connected by telephone and it is unmuted - even if it is just so you can make a comment to the class - you MUST turn off your computer speakers. If your speakers are on the sound coming in to you from the classroom gets picked up by your phone and fed back into the classroom, then back to you through your speakers, into the phone, and so on, and so on, ad infinitum.