It doubles your thorn damage. That's it.
Maybe there will be more use for it later (after release).

when you get hit your thorns gets triggerd twice

Originally posted by 60:

i dont get it

When you get hit, anything that does retaliation damage (which is only thorns in the demo), does it 1 extra time for each stack of chopsticks. So if you have 1, you'll deal your thorns damage 2 separate times.

Does throwback count as retaliation damage?

It's hard to know, unless you can tell which rocks are from Throwback.