The first lines to the Beatles song "I Want To Tell You", written by George Harrison.
'I don't mind,' Hal says. 'I could wait forever'. These are further lyrics to the song, though not the next ones.
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Toblerone is a Swiss chocolate bar, known for its triangular shape, based on the Swiss Alps.
Wallace referred to the confectionery in his 1990 essay 'E Unibus Pluram: Television and U.S. Fiction', pointing out that treats are acceptable but only in moderation: "One can only guess at what volume of gin or poundage of Toblerone six hours of Special Treat a day would convert to". The essay can be found in A Supposedly Fun Thing I'll Never Do Again.
Tosca is an opera by Italian composer Giacomo Puccini (1858-1924).
This is referred to again much later in the book (page 896 - "There is no music for free-floating misery like Tosca") just before Hal's facade of emotional antipathy (prompted by his father's death and sustained through years of drug-use) finally slips, and he feels "some variant of the telescopically self-conscious panic that can be so devastating during a match."
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Vissi d'arte from Tosca