Mute... or loudspeaker?
Many years ago, back when I still had a physical phone and headset on my desk, I took a phonecall from someone who's technical knowledge and skills were somewhat lacking. During the conversation, I hit mute to double check with someone about the finer details about how this person's request was completely impossible and then carried on with various repetitions of "Nope. Nyet. Nein, No.".
It took a while to twig I'd hit the loudspeaker button, and that everyone nearby could hear both sides of the conversation. Thankfully, they all agreed with what I was saying ;)
A few years later, I rang someone up who got confused and thought he was talking to someone /about/ me, rather than directly to me. Luckily, it turned out that he didn't have anything negative to say about me :D
In general, the company in question was very keen on the pushing people to be home-workers (cheaper than paying for office space) and making use of conference calls to reduce travel and expenses costs. Between the two, it wasn't uncommon to spend the entire working day glued to a phone, while listening to people dealing with their babies, pets, house alarms, etc.
And on a few notable occasions, you'd get someone who'd spent a little bit too much time on the phone, fallen asleep and started snoring...