The following lines are from “A Punch-Up at a Wedding,” the eleventh song on Hail to the Thief:
the pointless snide remarks
of hammerheaded sharks
The traditional phrasing is “hammerhead shark” rather than “hammerheaded.” The adjective “hammer-headed”, according to the OED, was first used in Arthur Golding’s 1567 translation of Ovid’s Metamorphoses, Book VII, line 74.
Hammerhead sharks, according to this encyclopedia entry, are often observed “in inshore, brackish water.” The sharks are “both predators and scavengers.” As this page explains, only one of four hammerhead species is considered dangerous. The OED claims the first reference to hammerhead shark occured in an 1861 book titled British Fishes.