 SPOILER: They give the "real" Valentin liquid LSD which causes him  to go crazy ultimately restating that he is, indeed, Valentin  Mironov, before committing suicide by jumping through the glass  window. This is a reference to an actual event wherein (Frank  Olson), a US Army scientist died in a similar way, allegedly as a  result of his unwitting participation in CIA conducted LSD  experiments called MKULTRA.