The version of "Mack the Knife" that Bobby Darin sings is a relatively late translation by Marc Blitzstein. Blitzstein's English version of Die Dreigroschenoper hit the stage off-Broadway in 1954 and had a very successful six-year run. "Mack the Knife," or "The Ballad of Mack the Knife," was retranslated from the original "Die Moritat von Mackie Messer."
Blitzstein did a lot to jazz up the lyrics for the times. A translation from the 1930s had never caught on as a popular song even after a Broadway run. Blitzstein added "dear" at the end of many of the lines, partly to make up for the difference in syllables from German to English. He also came up with some of the most famous lines as we know them: Oh the shark has pretty teeth dear / And he shows them pearly white / Just a jack-knife has Macheath dear / And he keeps it out of sight. The literal German on these lines is quite a bit less colorful, going something like: And the shark, it has teeth / And it wears them in its face / And Macheath, he has a knife / But the knife one doesn't see. If those lines are truly scary-sounding in the German, it's certainly lost in literal translation. Blitzstein's graceful translation restored the song's real power, the power of bloody descriptiveness.
The effect of these little changes created the perfect material for a popular song. After all, people love a thrill—within limits, of course. Blitzstein did choose to remove the song's last two verses, the ones about rape and arson, which might have pushed 1950s audiences just a little bit past those limits: And the ghastly fire in Soho / Seven children at a go / In the crowd stands Mack the knife, but /He's not asked and doesn't know…And the child bride in her nightie / Whose assailant's still at large / Violated in her slumbers / Mackie how much did you charge? In fact, we're thinking those last two verses probably wouldn't make it far in a pop song even today.
This stuff actually puts a lot of gangsta rap to shame for creepiness content, although it certainly has some latter day contenders. The takeaway point is not so much that some songs are scarier than others, but that being sinister—and knowing when to stop or slow down—really is an art all its own.