The thumb is motorized and connected by cables to a bracelet. Pressure sensors underneath the wearer's feet connect to the thumb's motors via bluetooth. So, working the extra digit just requires you to press down with your foot. Clode said that she linked the thumb to foot controls because with actions like driving, using a sewing machine or playing piano, we already have practice completing tasks that require hands and feet to work together.
Clode says the project is meant to explore how we can add capabilities to our bodies with prosthetics. "The origin of the word 'prosthesis' meant 'to add, put onto', so not to fix or replace, but to extend," Clode said to Dezeen, "The Third Thumb is inspired by this word origin, exploring human augmentation and aiming to reframe prosthetics as extensions of the body."
In the video of The Third Thumb, which is just a prototype, people use the extra digit while playing cards, carrying wine glasses, cracking eggs and even playing guitar. Overall, extra appendages feel like a move towards Orphan Black's "Neolution", but The Third Thumb seems much less permanent and way less creepy.