There can be various reasons why you are catching the skin.
1- is improper stretching of the skin by your client but if this is happening with everyone you are working on then it could be something esle.
2- if you are heavy handed. Do not apply pressure on the skin, the thread merely glides on the skin. The thread is kept taught but without pressure downwards onto the skin.
3- Sometimes if you pull back to slow or hesitantly (with mouth, if thats the method you use). Pull back needs to be even (not in stages) and fairly fast.
Hope that helps. Keep going with it, it is well worth the effort.:wink2: