Our chain is considered closed links. The 1.6mm chain links could technically be forced open to shorten or add something, but that could compromise the integrity of the link.
When we design toys with chain, we cut the length using wire cutters, and to add items we utilize O-Rings (http://makeyourownbirdtoys.com/O-Rings_c_27.html). We have a video about How To Work With O-Rings to help if you have questions: http://makeyourownbirdtoys.com/Videos_ep_48-1.html
Thanks for writing. If you have further questions, just let us know!