Depending on how you look at them, breasts can take very different shapes.
Bare busts can be eroticised or neutral, a symbol of women's liberation or their oppressive objectification.
Perky, ample bosoms are held up as a feminine ideal in popular culture,
but those in possession of them report discrimination at work and other negative effects.
They are glorified as sources of sustenance for infants: the World Health Organisation preaches that "breast is best",
and doctors call the milk "liquid gold" for its nutrients and antibodies.
In some countries, however, those who nurse in public attract uneasy glances, sometimes even reproof.
Breasts, Sarah Thornton avers, are both ogled and strangely overlooked:
"Mine had been hanging out under my nose for 40 years before I began to contemplate their significance."
She begins "Tits Up", an excellent new book with a bad title,
by recounting her experience of a double mastectomy and reconstruction in 2018.
She decided to undergo this procedure after years of biopsies and monitoring, owing to a family history of cancer.
To her dismay her request for "lesbian yoga boobs"—implying an unobtrusive size between an A and a B cup—goes unheeded.
The surgeon fits her instead with sizeable Ds.
She is irritated that her cups runneth over,
lamenting the presence of these "silicone aliens", their bulk and lack of feeling,
and how they change her sense of her own personhood.
What follows is a four-year quest to seek "the multifarious meanings and uses of breasts".
Ms Thornton, a sociologist and former contributor to The Economist,
identifies five places where women's chests are revered: