If the cat is in the same room as me, or within 20 feet outdoors, I will meow back without thinking, and try as hard as I can to exactly match the meow they do, in pitch, length, volume, everything. It's completely involuntary. Which is one of the only reasons why I'm glad my old cat that used to meow back at me EVERY TIME is gone. I've had meow contests with her that lasted anywhere between 15 minutes and 2 hours before, until either she left the room, or I threw her out.