Jubjub birds periodically "scream shrill and high", frightening all monsters on the level and stunning the player character. Any pets that are frightened by the scream also have their tameness increased by one.
But the valley grew narrow and narrower still,
And the evening got darker and colder,
Till (merely from nervousness, not from goodwill)
They marched along shoulder to shoulder.
Then a scream, shrill and high, rent the shuddering sky,
And they knew that some danger was near:
The Beaver turned pale to the tip of its tail,
And even the Butcher felt queer.
Such friends, as the Beaver and Butcher became,
Have seldom if ever been known;
In winter or summer, 'twas always the same—
You could never meet either alone.
And when quarrels arose—as one frequently finds
Quarrels will, spite of every endeavour—
The song of the Jubjub recurred to their minds,
And cemented their friendship for ever!