Alexander de Cova - Symbolicus (A Mental Routine)
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Effect:

You display a big envelope with a prediction. Two spectators assist you with this
experiment. You display now a transparent clipboard with a single sheet of paper on it.
On this paper are printed 25 different abstract symbols in a numered grid. You ask one
spectator to think of any uneven number from 1 to 25 (including 1 and 25). The other
spectator thinks of an even number. These numbers are only thought of!

Now each of the spectators looks at the clipboard and remembers the symbol
corresponding to his number. Again the spectators never name aloud their symbols
and you don’t ask a single question!

The prediction is read aloud: I， Mr. XXXXX， predict that tonight two vonlunteers will
absolutely free and without any influence from my side decide randomly on an abstract
symbols each. These two symbols will be a cross and a square.“

The two spectators indeed verify that they have been thinking of a cross and a square—
your prediction proved to be correct!