Answer:
Ryan is employing the defense mechanism known as displacement.
Step-by-step explanation:
Displacement is when one's feelings towards a specific target are redirected to a different one since it becomes less threatening. In Ryan's case, creating a conflict with his sister might give way to more issues. Being strict with the dog does not represent a conflict to him, it is not a threatening presence so Ryan and it allows him to discharge the negative feelings he has towards his sister in a more passive way.