3

Some people are more susceptible to this trick than others, so try on a few other friends if it didn’t work the first time.

If the trick works they will probably look surprised, gasp, or make some sort of exclamation. If they don't seem to react, you can ask, “Do you feel that?” in an expectant voice. If they don't feel anything, casually explain that it doesn’t always work on everyone, and suggest they may have opened their fist too quickly, or not clenched it tightly enough in the first place.