The number line provided shows two arrows pointing towards the left, indicating subtraction. Let's break down what we see:

1. Starting Position of First Arrow: The longer arrow starts at -1 and moves leftward to -13. This means we are subtracting a value from -1 to get to -13.

2. First Subtraction Expression: From -1 to -13, the difference is 12 units. So, this models the subtraction expression: $-1 - 12 = -13$

3. Starting Position of Second Arrow: The shorter arrow starts at -1 and moves leftward to -5. This represents a different subtraction operation.

4. Second Subtraction Expression: From -1 to -5, the difference is 4 units. So, this models the subtraction expression: $-1 - 4 = -5$

Hence, the number line models two subtraction expressions:

1. $-1 - 12 = -13$
2. $-1 - 4 = -5$

Would you like more details on how to interpret the number line or explore related topics?

Here are some related questions for further exploration:

1. How do you interpret addition on a number line?
2. What is the significance of direction in number line operations?
3. Can subtraction on a number line result in positive numbers?
4. How would the number line change if we used positive numbers?
5. What other operations can be visualized using a number line?

Tip: When subtracting on a number line, always remember that moving to the left decreases the value, while moving to the right increases it.