Were you clear in your initial instructions/suggestions? It can help to get an explicit agreement from them that they have understood. Additionally, I have found that it helps to nod as you shake, to confirm what they should do.
However, there is no point carrying on to the 3rd shake, if they are clearly not even responding to the first one. In this case, you do not want to imply failure on anyone’s part. Instead, you will change your shake from single to continuous, or vice-versa as you go through the directions again. Your patter may sound something like this, as you give the impression that this is an experiment that you are both working on and with which you are both interested in the results and determined to succeed.
“Well, I can see that your subconscious is alert and active. [Smile] …And we can use that… So, I suspect that we will have more success if we do it this way…”[Explain the process again, with an alternate type of shaking. As you state what they will do each time, nod your head. This will often elicit a nod from them, confirming that they understand.]
“You’ve got this.”
Notice that you are direct this time, even if you were permissive the first time around.