What is this flat dry stick-like leaf that rattles?
I believe this a seed-pod from an Inga or Delonix plant.

Inga are native to South America, while Delonix are native to Madagascar. But they've been introduced to other places and I've seen similar plants in the northern hemisphere. Inda and Delonix are both members of the subfamily Caesalpinioideae. I found the name by searching for "seed pod shaker". Sometimes you just need to know what terms to google.

Shown in the image below is pacay, or Inga feuillei.



But your pod could also be from the flame tree, Delonix regia.