Sperm whales do not "sing." Their vocalisations are rapid series of clicks.
When apologising to Hughie for hitting him, Billy says "I lost me bottle a little bit when I popped you one."
The idiom to "lose your bottle" means to lose nerve, or to become afraid. There are various things that Billy could have "lost" when angry, including his "rag" or his "head" - but his bottle would not be one of them.
The idiom to "lose your bottle" means to lose nerve, or to become afraid. There are various things that Billy could have "lost" when angry, including his "rag" or his "head" - but his bottle would not be one of them.