Peregrinus Expectavi Pedes Meos In Cymbalis

Peregrinus expectavi pedes meos in cymbalis. A silly (when translated) and grammatically-incorrect nonsense Latin phrase which the composer Sergey Prokofiev used as one of the lyrics in his score for the 1938 propaganda film Alexander Nevsky. This is notably heard in the background as the Teutonic Knights charge towards the army of Russians during the Battle of the Ice:


(clip with better audio viewable here)

Many people have attempted (and failed?) to decipher this short elusive phrase (which is otherwise unattested in Biblical, Patristic, Ecclesiastical, or indeed even secular literature), often with strange results; while others just deal with it briefly and never mention it again, shrugging it off as either an obscure medieval hymn - which would be odd, since were it a true hymn we should either be singing it in church right now or have manuscripts that give its lyrics! - or a feeble attempt by Eisenstein and Prokofiev at concocting a Latin phrase and coming up with nonsense (Prokofiev originally intended to use authentic medieval chant for the score, but found the music "so far removed" and "emotionally alien" to the 20th century listener).
However, Morag G. Kerr, soprano for the BBC Symphony Chorus, may hold the true answer to this riddle: the nonsense phrase is actually a jab against Prokofiev's colleague-slash-rival Igor Stravinsky, who wrote The Symphony of Psalms in 1930. The Latin words of the phrase are apparently taken from phrases found in the Latin Vulgate, specifically, from Psalm 39:12-13 [38:13-14]; Psalm 40:1-3 [39:2-4]; and Psalm 150 (this can be observed here). The clincher is, these are the exact same Psalms Stravinsky used in his symphony, so saying that it is coincidental would be rather unsatisfying.

Random minor trivia: In the clip above, a keen observer would notice that the Teutonic bishop blesses/makes the Sign of the Cross in the Eastern manner (moving from the right shoulder to the left) as opposed to the present-day Catholic left shoulder-to-right movement!