Around minute 8:44. When I do it, my right constrain says left. So it won't work. When check your video again I see the you name says RIGHT instead of right and per the bone you are selecting. And when you click back to the left it says LEFT instead of left a per the one you are clicking. Don't know it feels a bit confusing. Anyway I'll carry on watching the video it might fix itself.... ;-)
Hi Sergio,
Perhaps the thing that you are confused with is the difference in the bone names and the target names.
The bone I am selecting is ends with "_left" (or "_right") BUT the name of the target bone is different. It ends with "_LEFT" (or "_RIGHT")
The names in the constraint are not the names of the bones I am selecting.
Hope that makes sense.