Answer
The difference lies chiefly in the seriousness of the resulting harm and the length of the resulting incapacity or medical treatment. Serious physical injuries (Article 263) are the gravest — they cause the loss or uselessness of a body part or sense, insanity, deformity, or an illness or incapacity for labor of more than 30 days. Less serious physical injuries (Article 265) cause incapacity for labor or require medical attendance for 10 to 30 days.
Slight physical injuries (Article 266) are the least grave — incapacity or medical attendance of 1 to 9 days, or injuries that cause no incapacity at all (such as maltreatment without other injury). The classification determines the penalty: the graver the injuries and the longer the incapacity, the higher the imposable penalty.