'I Heart Huckabees' (2004)
David O. Russell's beautifully bizarro "existential comedy" casts Hoffman as one half of a detective team (along with Lily Tomlin) who are hired by a young man to investigate why he keeps experiencing these metaphysical moments of uncertainty. A damaged firefighter (thank you, Mark Wahlberg!), a department store head and a former pupil of the couple start to throw their own oddball Zen mantras into the mix. And then things get truly weird. Blessed with a shaggy hairdo that instantly gives him an absent-minded-professor vibe, Hoffman isn't just game for playing with the director and co-writer Jeff Baena's Philosophy 101 brain teasers; he seems positively giddy to be involved. And his monologue about "blanket truth," in which he outlines how we're all interconnected under the surface, is a keeper.