Master of Vertical Maneuvering

Rittai Kidō no Shi (立体機動の師) is an extra chapter included in the 8th volume of the Attack on Titan: Before the Fall manga, written by Ryō Suzukaze and illustrated by Satoshi Shiki.

Overview
Kuklo, struggling with his skills in vertical maneuvering, finds the answer to his problem after observing a cat chasing a mouse.

Summary
On the day before testing the Device at nighttime at Wall Maria, Kuklo struggles with visualizing how to make his body react to sudden changes of direction when using the Device. Cardina suggests a combination of vertical and horizontal wires might be necessary, but is unsure of his guess. Suddenly, Kuklo spots a cat chasing a mouse. When the mouse suddenly runs off in another direction, Kuklo notices how the cat moves its upper body in midair while chasing after the mouse, maintaining its speed. Kuklo catches the rat in the air, enthusiastic about his discovery. He thanks the cat, referring to it as "Master", and offers it the rat. The cat contently walks away, and Cardina suggests that the cat is letting him keep the rat as a reward.