Answer
The light rays on the left side of the object are reflected first by the left mirror to the right mirror, then by the right mirror to the right side. Therefore, it seems as though the left side of the object is actually on the right side.
Work Step by Step
According to the law of reflection, the angle of incidence is equal to the angle of reflection. This means $\theta_1=\theta_2$ and $\theta_3=\theta_4$. However, because the two mirrors form a $90^o$ angle, by symmetry, $\theta_2=theta_3$. Thus the light rays on the left side of the object are reflected first by the left mirror to the right mirror, then by the right mirror to the right side. Therefore, it seems as though the left side of the object is actually on the right side. The same is true for the light rays reflected off the right side of the object.
