Knex Hidden Blade from Assassin's Creed. I only used basic pieces with minor/optional modifications. I also used string for the trigger and rubber bands to move the 'blade.' Taping the bottom of it is optional and makes it more comfortable in my opinion.
Step 1: Parts
2 Red Rods
1 Grey(Black) Rod----*I do not know how it will work with a grey rod. The black rod is stronger.*
1-2 Green Rods---*These can be used on the locks to stop them from spinning completely around.
7 Orange Connectors
15 Grey Single Connectors---*Some are optional, just used to hold the rubber bands*
3 Small Blue Spacers
3 Larger Grey spacers----*Grey spacer = 3 small blue and they can be substituted*
2 Rubber Bands
String---*Length Varies from person to person*
Tape for comfort