The counter model visually explains the subtraction of integers with opposite signs by employing the concept of introducing neutral pairs.

• For the expression $-7 - 4$, we start with $7$ negative counters, but need to remove $4$ positive counters. Introducing $4$ neutral pairs allows us to remove the required positive ones. The leftover counters are $11$ negatives, showing that $-7 - 4 = -11$.
• For the expression $7 - (-4)$, we start with $7$ positive counters, but need to remove $4$ negative counters. By introducing $4$ neutral pairs, we can remove the negatives, leaving a total of $11$ positive counters. Thus, $7 - (-4) = 11$. These instances further demonstrate how the introduction of neutral pairs converts subtraction into addition of the opposite number.