Cas Cas are two seed pods joined by a string. They are often played in pair traditionally by the Ga tribe in the South of Ghana. One ball is held in the hand while the other is swung around the hand, cracking against the other. 
 
This is an amazing Ghanaian instrument. Watch out, it’s pretty addictive. Search cas cas shaker on YouTube to see how they are played. 
 
£16 for two (ie 4 seed pods)