Katy Perry called herself a 'tough mom' as she judged two teenage contestants on Monday's second Hollywood episode of American Idol.During the duet rounds, the 36-year-old singer advised Laila Mach, 15, and Liahona Olayan, 17, on their cover of Rihanna's Stay.It was 'sludgy,' Katy told them during rehearsals, noting that the girls seemed like they were dragging their heels just to be there.
