 Placebo needle is a useful tool to assess the efficacy of acupuncture. Investigators have applied a new kind of placebo needle in large scale acupuncture clinical trials, which named as pragmatic placebo needle. Compared with other placebo needles used in acupuncture trials, this pragmatic placebo needle shows several advantages: the outlook closer to traditional acupuncture needles, no restriction to needle depth of true needle, simple to manipulate and more economical. However, its blinding effect is not yet validated. The primary objective of this trial is to validate the blinding effect of the new pragmatic placebo needle; the secondary objective is to explore factors influencing the blinding effect of the placebo needles. 