Indestructible String

Effect: A string is threaded through a drinking straw. The straw is cut in two but the string remains unharmed.

Secret: Secretly cut a short slit in the straw. Thread the string through the straw. Bend the straw in half and pull both ends of the string. This forces the string through the slit in the straw. Your hand hides this from the audience. Cut through the straw, as shown by the dotted line in the drawing. Now pull the string from your hand. The straw is in two pieces but the string is still whole.