When stuck in a conversation with a stranger who loves to hear the tone of his/her voice, do the following to give off the illusion that you are really engaged in the conversation between them and themselves.
1. Nod
Nod your head for the hell of it. Continue nodding to each eye contact to make them think that you are both on the same page of the conversation. Alternate speeds too. Sometimes, make it fast. Sometimes, make it slow. Just don't stop shaking.
2. Make sounds
Seriously, making sounds will egg them on. The conversation will continue for as long as they like because you can't really walk away and there's no phone in sight. If you are anything like me, you cannot pass up the opportunity to experiment with different forms of entertainment. Since They also have not bothered to acknowledge your input in the conversation, continuously make sounds like mmm, and shhh, or even oh ahhh whenever you feel like it and watch them think they are in the most delightful conversation.
3. Blow Air
Just do it. Those sounds would fit perfectly anyway, seriously. Just do it, trust me.
4. Facial Expressions
Lastly, include facial expressions To accompany these suggestions. Let the talker know your interest in the one-sided conversation is fo'real!
Sometimes people like to vent to strangers and it is not your fault. You can help them out, and also have a little fun :)