Explain why in Levine’s experiment (Example A in Section 11.3.1) subjects also smoked ci...

Explain why in Levine’s experiment (Example A in Section 11.3.1) subjects also smoked cigarettes made of lettuce leaves and unlit cigarettes.

Reference

To study the effect of cigarette smoking on platelet aggregation, Levine (1973) drew blood samples from 11 individuals before and after they smoked a cigarette and measured the extent to which the blood platelets aggregated. Platelets are involved in the formation of blood clots, and it is known that smokers suffer more often from disorders involving blood clots than do nonsmokers. The data are shown in the following table, which gives the maximum percentage of all the platelets that aggregated after being exposed to a stimulus.