Mexican director Alejandro González Iñárritu (2000's Oscar-nominated ''Amores Perros'') has decided to come out swinging in his $20 million English-language debut by casting some Hollywood heavyweights. Naomi Watts plays a grieving mother whose life intersects with terminally ill mathematician Sean Penn and ex-con Benicio Del Toro following a horrific tragedy. And that's about all Iñárritu will reveal. ''It's about three people dealing with their own personal hell, trying to survive their own demons,'' he says, sighing. ''It's just too complicated to describe.'' (Rounding out the cast is Charlotte Gainsbourg, who stepped in as a replacement when British actress Katrin Cartlidge died unexpectedly last September.)
Watts, however, will elaborate on the odd title: ''[Twenty-one grams] is the amount a body loses when one dies, and that's allegedly the weight of one's soul,'' she explains. (Perhaps the nod to the metric system will help when the film competes for the Golden Lion at the upcoming Venice film fest, where it's one of only two American contenders.) But if the plot seems awfully familiar -- a car accident was also the catalyst in ''Perros'' --it's because screenwriter Guillermo Arriaga penned both films. Warns Watts: ''['21 Grams'] is even more raw.''
The Killer Moment ''A car accident that, for god-awful reasons, binds the three characters together,'' says Watts.