Ask your partner to think of any two digit whole number and not tell you what it is (minimum is 10 and maximum is 99)

Ask your partner to cube their two digit number and tell you what the big cube number is (for example, if your partner picked 47, they would cube 47 by calculating 47*47*47 and giving you that big cube number.

You would surprise your partner by looking at their big cube number and successfully "guessing" what their original two didit whole number is.