Warning: Beginners should not attemt this technique. Even experts should proceed at a very slow pace when going down past the wrist.

Keep a closed fist and slowly delve deeper and deeper into the canal. Make sure to keep any new area you insert well lubricated. Slowly work your way as far down towards the elbow as you can. Watch your partner closely because most people can't make it very far. The idea is not to actually get to the elbow (very few can actually do that), but to go in that direction and enjoy the pleasure of a deep probing.