The sum of $-8 + (-1)$ is calculated as follows:

$-8 + (-1) = -8 - 1 = -9$

So, the sum is $-9$.

Would you like more details or have any questions?

Here are 5 related questions:

1. What is the sum of $-10 + (-5)$?
2. How does the sum of $-8 + 1$ compare to $-8 + (-1)$?
3. What is the result of adding $-8$ to itself?
4. What happens when you add a negative number to a positive number of equal magnitude?
5. How would you express the addition of two negative numbers on a number line?

Tip: When adding two negative numbers, think of it as moving further to the left on the number line, which results in a more negative number.