Algodoo

A crossbow using a weakened 1.9.9 chain (black) to create an elastic force
to pull the arms outward. There are somewhat realistic arrows to put in it (check the nocks), but they're bow arrows, not crossbow arrows. The crossbow doesn't have a bowstring latch or anything anyway, so it's like an extended arrow-rail compound bow.

Instructions:

Grab an arrow.
Place the arrow nock first into the rails
Pull the arrow back until it can't go further
Release the arrow, and repeat as many times as needed.

This scene works at a frequency of 100Hz, which is good because I've been uploading way too many 500Hz scenes.