So what if fish require water to survive? Flirting on the sand of a moonlight beach is seductive to certain pufferfish (in bursts). That isn’t the only strange thing the ocean’s famed self-inflators do. Some of the 200 or so species in the puffer family go to great lengths to court.

On a few moonlight nights each year, Japanese grass pufferfish (Takifugu niphobles) congregate on Asian beaches to mate. “A gigantic ball of these pufferfish, maybe 400 fish,” says Gareth Fraser, an evolutionary developmental biologist at the University of Florida in Gainesville.

Typically, he explains, the ball includes several hundred males and maybe one female. Males begin to leap about, spilling spe.rm into the wet sand where a female releases eggs. When a large enough wave sloshes in, it sweeps them back out to sea. Underwater sand is also appealing. Males of a previously unknown species were discovered to be the architects of enigmatic underwater crop circles in 2014.

Torquigener albomaculosus (white-spotted pufferfish) spends days plowing and fin fanning sand into large symmetrical rosettes as welcome mats for female visits. Pufferfish courtship, on the other hand, maybe harsh, according to Fraser.

“Occasionally, the male will bite the ladies’ abdomens with these incredibly sharp beaks.” Fraser’s scientific curiosity was piqued by those odd beaks, which were more parrot-like than shark-like. The initial teeth of newborn puffers appear to be vertebrate.

However, when the fish grows older, the rows of pointed parts give way to two nubs that spread sideways along the jaw, eventually becoming a pair of long, sharp-edged blades. Adult puffers “can slice a fish in two and then feast on it,” he adds, with one pair of blades along the top jaw and another on the bottom. Aquarists should feed their pufferfish hard-shelled mollusks to wear down the blades or cut them back using a fish equivalent of a nail clipper.

The fish cannot feed if their beaks become too large. Pufferfishes are arguably most recognized in the scary body part repertoire for transforming into spiky balls when provoked. When puffers inhale water to expand their abdomens, their spines pop up.

Fraser and colleagues report on July 25 in iScience that some of the same gene networks that produce feathers in birds and hairs in humans also produce protective spines in puffers. Those spines developed from scales covering distant fish relatives. Modern pufferfishes, on the other hand, are completely bare between their slender spines. Make an effort not to look.