It only moves forward because there is a net force forward.
Explanation:
In this scenario, the forward force (5 N) minus the backward friction force (4 N) results in a net forward force of 1 N. The vertical forces (10 N down due to gravity and 10 N up from the animal's push) cancel each other out, resulting in no net vertical movement. Therefore, the animal moves forward with a net force of 1 N.