'M' as in Mathieu(M comme Mathieu)

Mathieu is collected from the hospital by his wife, and dropped of at an apartment. His wife returns home to their son. The next time she sees him, he confesses that he is in love with another woman. This woman, who is identical to his wife, visits him. After making love, she leaves. She then returns. Mathieu shoots her - or does he shoot a mirror?