Cassie gave Violet a nod of acknowledgement for erecting the forcefield that pretty much saved her from becoming a pancake.

Seeing Mako's attempt to cleave the Omnidroid with her katana, Cassie wanted to see if she could help her in that regard.  Despite the sheer amount of noise being generated, Cassie was still able to 'hear' the sound of Mako's sword vibrating, reminding her of the 'cooking' attempt she made in the kitchen.  Realizing that Mako was trying to superheat her katana through magnetic vibrations, Cassie helped with sound vibrations by switching her acoustic traps to match the sword's vibrations. Maybe it would help the blade slice into the robot's hard metal shell, or maybe the blade would shatter from the stress.