It's enough to give Agathe an opening, with the thing distracted. She stomps hard on the back of its knee as it lurches after Arthur, and in its tenacity, the mannequin's leg joints begin to separate.
Spotting the opportunity, Agathe seizes it by crouching to drive her knife into the hip joint, crunching gruesomely away (it's not like it can feel pain) as it doubles back once more, trying to manage a proper angle of attack.

"Hold it down," she calls to the man, frantic and determined.