The perfect gag card...in JUMBO size.
The magician says he'll find a card equal to half of the card selected by the spectator. Since the spectator selected the 7 of Clubs, this feat proves impossible.
Until the magician produces the 3 and 1/2 of Clubs!
NOTE: No instructions...this requires a force of the 7 of Clubs, and control of the 3 1/2 of clubs.