Someone suggested that the three words actually have a meaning – “The scorpion bit the uncle”… ingenious but impossible.
It is not well known that these words actually formed part of the stock in trade of the antisemites who accused Jews of using Christian blood for wine or even to mix the matzot for Pesach. As often happens the antisemities exploited the Jewish knowledge that renegades brought with them when they left the Jewish fold.
Chayyim Bloch recounts in his “Ostjudische Humor” that a Russian Imperial Commission once summoned Rabbi Yitzchak of Volozhin to answer charges against Judaism and quoted against him the word D‘tzach as meaning, Dam Tz‘richim Kulchem – “everyone needs blood”.
The quick-thinking rabbi turned the allegation against the questioners by saying D‘tzach Adash B‘achav stood for Div’rei Tzor’renu K‘lum, The words of our accusers are nothing; Alilat Dam Sheker, the blood accusation is false; B‘nei Avraham Chalilah B‘Zot, God forbid that the Children of Abraham should do such a thing!”
Unfortunately the blood libel still surfaces from time to time even in Christian circles, though the Vatican endorsed in the 1930s Cecil Roth’s edited version of Cardinal Ganganelli’s detailed analysis and repudiation of the accusation.