In the 21st century, even when states sanction their interrogation methods, torturers often work outside the law. For this reason, some prefer methods that, while unpleasant, leave victims alive and unmarked. A victim with no visible damage may lack credibility when telling tales of torture, whereas a person missing fingernails or eyes can easily prove claims of torture. Mental torture, however, can leave scars just as deep and long-lasting as physical torture. Professional torturers in some countries have used techniques such as electrical shock, asphyxiation, heat, cold, noise, and sleep deprivation, which leave little evidence, although in other contexts torture frequently results in horrific mutilation or death. However, the most common and prevalent form of torture worldwide in both developed and under-developed countries is beating.