Have a partner press the knife tip to you and allow the tip to move you as a whole without tensing or trying to navigate away at first. You may try to compare trying to work straight away without relaxing and feeling and note where you feel the blade run deeper. Once you clean part of the fear of penetration move along the initial  relaxation movement and feel where it is safer to be. Keep breathing and moving with your body even if your limbs are under the knife to avoid tensing up and allow the blade to run its course without you giving it any support (tension and resistance)
Next have your partner do the same to you and at the same time press his hand or fist to your head. This will allow you to better feel where you bend and twist yourself and you will be able to move more with and guide your partner rather than trying to outsmart or out maneuver him.

You may than add an arm or any limb to the work to help the body work rather than work with your arms and letting the body parish in static. Remember life is movement and movement comes from the breath.