When an interviewer asks this, he or she is merely digging for a reason to turn you down. Applicants can be so accommodating. The pressure of tests causes me to freeze up. Many job candidates will tell the interviewer about a failing or weakness that generates a sure turndown. Sometimes I'm impatient with others whose standards are not as high as mine.
Interviewees show their true colors.
First of all, I want to learn your business from the ground up. Long term, I hope to be in a position of greater responsibility that is mutually beneficial to the company and to myself. Any negative about a prior employer is an absolute turndown immediately. Bad apples offer sour grapes, to mix a metaphor. The employer is fishing for information here.