In Greek mythology, Scylla and Charybdis were two sea monsters situated on opposite sides of a narrow channel of water. Perhaps they were the personifications of treacherous rocks and a dangerous whirlpool in the Strait of Messinia. Avoiding one put sailors at risk from the other. The phrase "between a rock and a hard place" likely derived from the phrase "between Scylla and Charybdis."
Dire Straits
Dashingly-Swirlingly
Scylla --Charybdis, too--
Rock and a hard place of
Homeric fame,
Physical features are
Anthropomorphously
Merged into monsterous
Women in name.