Well this is indeed a great effect. The secret is easily concealed and almost self working, HOWEVER,
it is so easy to perform, that you might underestimate the danger that lies in the psychology when
performing this effect.
We, as magicians, usually want to find what we look for (a card, a
thought etc). This time you honestly want to avoid the cup with the spike. You might get confused
for a second about what you want to do with the information you clearly hold about where the spike
lies, and a second is all it takes... That's why I took one star off.
Actually, I've
mainly wanted to leave a review, to ask the one guy that reviewed that trick before me, back in
2010, to PLEASE let us know he's still alive.
When it comes to this trick, by all means,
use your head. But please, not in that way.