in your mouth but do it before you pull the twist tight together.....that way when you pull it tight there's no friction. Ie. 40-50 turns, lubricate then put it on your foot/feet.
I do my reverse twist abit apart half way down then close together for the rest, then half hitches and the finishing.....
You'll find more than 90% of the time it breaks about 5cm from the knot without lubrication.