how did this guy make his wolverine claws retract?

hi guys so wolverine isn't far away now (6 months will fly lol) and i wanted some claws to accompany me to the cinema now ive seen plenty of claws the retract with a draw slider but they have to lift there arm to make them retract this guys one just retract with a simple hand gesture :/

Retractable Wolverine Claws - YouTube

im assuming its simply flexing as he has nothing on his hands but i really can't figure out how he made them any tips be great peace bub