Thompson effect 

Phenomenon in which one stops listening to conversation for a short interval of time, only to find it has strayed wildly from the original topic

idle chatter: ...so then we were riding the bus and...

*stop listening for 15 seconds*

idle chatter: ...the soy-based tear gas substitute worked really well because...

listener: fuckin Thompson effect, I have no idea what's going on.

Thompson effect by dgran August 31, 2008