ending

Essentially, it's just a surreal sight gag. The Fox escaped the first time by posing as the doctor visiting his cell, pretending to have been bound and gagged by the real Fox. This time around, he instead leaves the doctor tied up in his cell and walks out in his place, including disguising himself with a fake beard. We then see him calmly walking out of the prison. Normally, we would expect to see him pull off his fake beard, smile, and walk off into the sunset. But instead when he tries to remove his "fake" beard, it won't come off. It is obviously a real beard now. Since the Fox knows he didn't have a real beard before and does now, he can only come to one bizarre conclusion: he must be the doctor and not himself. He shouts, "My God. The wrong man has escaped!" It's not supposed to make sense - it's just something to make you laugh.