The first test case has all valid indexes so if you pass the first test, you've understood how to extract the letters for the secret message as long as the index in the numbers list is valid.
The test cases have both valid and invalid indexes that are both positive and negative. You need to make sure the index is valid before you try to use it to access the letter so that you won't have an IndexError.
So when is the index valid? It depends on the word you are trying to index. There is a certain range of indices from a particular negative integer to a particular positive integer that are valid for each word. You need to figure out that valid range.
