eavesdroplet - A tiny piece of a secret conversation that you eavesdrop on

A tiny piece of a secret conversation that you eavesdrop on while pretending you're not listening.

I heard 'I told you to stop eating my chips' from the kitchen.

She whispered 'He's gonna find out' while I was pretending to check my phone.

I caught 'I'm not even mad' from the copy machine.