Subject: Please suggest a control for an experiment on ticklishness?

I am doing an experiment to prove that we are far more ticklish when we don't 
know we are going to be tickled than if do - I am using 40 people for this 
experiment and will tell half of them that they are going to be tickled and 
then tickle them for 10 seconds, and not tell the other half, just ticklet 
them with no warning for ten seconds - and compare how many people laugh in 
each group - What would be a control for this experiment and do you have any 
suggestions for measuring my results except by the number of people who laugh?

Re: Please suggest a control for an experiment on ticklishness?