Letters Simile
"A couple of lines or eight pages, a Middle Eastern stamp or a suburban postmark....I hoard all these letters like treasure."
The author is comparing the letters that he receives from friends to treasure, giving them a value to himself far greater than the value to the sender. Traditionally, treasure would be hidden away, often buried, to protect it, and to keep it safe, because it is so intrinsically valuable. He is comparing the value of his letters and contact with the outside world to treasure because it is priceless to him.
Banner Simile
"One day I hope to fasten them end to end in half-mile streamer, o float in the wind like a banner raised to the glory of friendship."
This is one of many nautical similes and metaphors that the author uses, as in traditional sailing regattas, banners made out of tiny flags were fastened to the masts of the tall ships in celebration. Bauby would like to make a banner out of the letters his friends have sent him, because they are a testament to the strength of their friendship and are also the only thing that has kept him going since tragedy befell him.
Rapier Metaphort
"The keenest rapier grows dull and falls flat when it takes several minutes to thrust it home."
This metaphor is describing the way in which the use of wit and sarcastic humor has become forever changed, and also obsolete, in Bauby's situation. Previously known for his weapon like wit, he could slice someone down to size like a swordsman plunging his sword into a challenger; however, now this rapier-like wit is wasted. He can still think of the repartee that formerly made others laugh, but cannot express it quickly enough for it to be witty anymore. He compares this to what happens to a rapier, which has a blade sharp enough to kill or wound but not when it is plunged into the body incredibly slowly. It completely loses its effect, and this is also what is happening to the incisive wit of the author.
Pressure Cooker Simile
"But to keep my mind sharp, to avoid descending into resigned indifference, I maintain a level of resentment and anger, neither too much or too little, just as a pressure cooker has a safety valve to keep it from exploding."
The author is comparing his own control over his emotions to the safety valve on a pressure cooker. It is the only thing within him that prevents him from unraveling emotionally or from exploding into anger that might get directed at other people; this is not what he wants to happen This is the same as the safety valve on a pressure cooker which enables an enormous build up of pressure to be diffused safely before an explosion occurs.
Caveman Simile
"The exhausting exercise left me feeling like a caveman discovering language for the first time."
The effort that re-learning how to speak takes the author is comparable to the effort it took to create a language in the first place. Bauby feels like a caveman with no education to fall back on; language for him, as it was for cavemen, is a new and unfamiliar experience that is daunting and a struggle. His tongue is being asked to make strange movements that are not yet known, and he does not feel like an educated, intellectual man with a wonderful grasp of the language, but like a neanderthal man who has never spoken before and who is trying to create and learn a new way of speaking with a tongue that has no muscle memory to fall back on.
