Ghidorah, The Three-Headed Monster humorously suggests that the King of the Monsters has a bit of a filthy mouth and actually swore at Rodan.
Released in 1964, Ghidorah, The Three-Headed Monster was the fifth movie in the franchise and a direct sequel to Mothra vs. Godzilla, which hit theaters earlier that year. Ghidorah, The Three-Headed Monster marked the first meeting between Godzilla and Godzilla and Rodan were recruited by Mothra to forces and drive off King Ghidorah.
The scene that led to the two monsters' act of heroism included a hilarious moment between Godzilla, Rodan, and the Godzilla, Rodan, and Mothra are able to defeat King Ghidorah.
Godzilla's use of foul language is a fun, light-hearted moment for Godzilla, which stands in sharp contrast to the awkward scenes in 1972's Godzilla vs. Gigan, where Godzilla actually speaks English. Ghidorah, the Three-Headed Monster shows why it's so much better not to know exactly what Godzilla is saying.
Of course, what Godzilla actually said to Mothra is never revealed, and considering the film's kid-friendly tone, that's probably a good thing. Indeed, humor in Ghidorah, the Three-Headed Monster isn't limited to Godzilla's swearing. During their first fight, Godzilla and Rodan basically played a game of volleyball by hitting rocks at each other with their heads. Later, Godzilla enjoyed a long, hearty laugh when Mothra sprayed Rodan in the face with its silk.
However, fans can expect a much different tone when the three protagonists of Ghidorah, the Three-Headed Monster return in Godzilla: King of the Monsters.