Hear
If you go up to a gate and press your ear to it, you'll hear what's going on on the other side. The people on the other side will have no idea you can hear their conversation.
ぶん, もん
き
None
From the other side of the gate, you hear one of the people start to play a song on a recorder. You recognize the song as "Hot Cross Buns (ぶん)." You haven't heard this song since grade school. "Hot cross buns, hot cross buns~"