Ashlee S. giggled through video shoot

ASHLEE SIMPSON struggled to film her latest music video INVISIBLE after developing a case of the giggles. Simpson took inspiration from HILARY SWANK's Oscar-winning performance in MILLION DOLLAR BABY to play a female boxer in the MARC WEBB-directed promo. The PIECES OF ME hitmaker admits she struggled to keep a straight face when she pretended to box. She tells MTV, "I giggle all the time, and I laugh at everything, and Marc told me to be tough and not laugh in the ring. That was difficult. "I had one day of training, and right now (on the second day of shooting) I'm one sore 'beyotch' (bitch)." [PRI]