A grocery clerk is astounding shoppers with his beautiful singing voice. 23-year-old Guilherme Assuncao was testing the new sound system at Russo's supermarket in Watertown, Massachusetts when he started to sing. Shoppers were blown away by his talent. Now video of him serenading customers with Christmas carols is going viral. Despite his obvious talent, the 23-year-old singer and grocery clerk says he still gets nervous performing in public.