I didn't know and just assumed that...))
Tris watched the two boys, her morphing freezing when she returned back to her usual appearance. However, when her fears were released into her mind, she began panicking, and panicking caused her to change into any face she had seen; whether she was actively aware of it or not. She let out a loud sigh of relief when it stopped and dropped to the floor, though she quickly pushed herself up.
"How do I know I can trust you?" She glared at the two of them.