Mint error coin? [opgelost]

Hello,
this evening got a half dozen coins, including this cruzeiro's 20 centavos coin, but one side is kind of "missing" (sorry for the image quality)

What is this, a mint error? And what the value of the coin compared to the normal one? (https://en.numista.com/catalogue/pieces5379.html)

Thanks in advance.

This was done post mint: the coins is made hollow to hide another coin, probably to do 'magical' tricks with it.

Recently there was another forum thread with examples of it:
https://en.numista.com/forum/topic62196.html

Citeer: "ArnoV"​This was done post mint: the coins is made hollow to hide another coin, probably to do 'magical' tricks with it.
​
​Recently there was another forum thread with examples of it:
​https://en.numista.com/forum/topic62196.html

​Hahaha! That's nice! What can I hide inside it? It's not much larger than an American penny (going to figure out later).

Thank you!

Edit: only very small coins are fit inside: the only current coin that fits it is a 1 centavo coin (2004, the 1994 version doesn't fit), other small coins that fits in are a 20 réis 1920, a 50 réis 1922 and a 100 réis 1942.