In Chapter 5, Twilight tries to conduct various tests on the bracelets' effects. When Rainbow and Fluttershy try to leave, she telekinetically gets out a long reel of rope and ties them both up.
Rainbow Dash was going to begin yelling obscenities to her magically gifted friend, but found herself saying something completely different. “Fluttershy, why are you smiling?”
“Don’t tell her you like being tied up, don’t tell her you like being tied up,” Fluttershy thought to herself as she looked to the pony she was tied together with and broadened her smile.
“I love being tied up.”
Silence descended on the room. Twilight stopped trotting towards her friends, Rainbow Dash did not say anything more, and Fluttershy stopped even breathing. Twilight had learnt of one of Fluttershy’s fetishes, Rainbow Dash had learnt of Fluttershy’s strange hobby, and Fluttershy was internally screaming at her slip of the tongue.