The shak-shak (or chak-chak) is a kind of Antillean musical instrument, similar to maracas or shakers.
The word shak-shak is also spelled as chak-chak, shack-shack, xaque-xaque (in Brazil), and chacha (in Cuba).
In the Greater Antilles, it is also known as a maraca, a term that has its roots in the Guarani word mbaraca.
They are often made of hollow gourds with beans placed on the inside to make the shaking noise.
[1] The shak-shak can be heard in the piece "Ol' Time Calypso" by Roger Gibbs.