"Last Visible Canary" is something I used while playing counter strike with a friend because he wanted me to play it with him. One of his favorite books as a child was "A Mouse and His Son". It's a story about a toy mouse (connected at the hands, the kind where the smaller mouse flips when you wind the larger mouse up) who lose their way after leaving their toy shop. at one point they are thrown to the bottom of a pond and are stuck there. There is a tortoise named serpentina who wrote a play called "The Last Visible Dog" that is later performed by 'the caws of art'. It refers to the label of a can of bonzo dog food, where a small dog is holding a bonzo can in his and, and that label has a dog holding the can, into infinity. The mouse and his son are stuck talking to the tortoise who speaks in hipster art lingo, and when the son asks how they'll ever get out of the lake, what is to become of them, she tells him that when he can find the last visible dog, he'll know. So he tries to the count the dogs, trying to see the tiny image past the 12th dog, but thats about as far as he can go. Until a current starts to rip the can at the center of the image, revealing the metal underneath. He proclaims "the last visible dog.... is me!". The vague concept being of self determination, that ones future is, at the very least, largely determined by their own choices rather then the physical problems around them.
The change to Canary takes what was just a side story of interest and makes it more personal. I'm not a miner, but I like the phrasing and the concept better. When your in a mine, if you have multiple miners checking pockets for methane/gasses, the last canary you can see is the edge of your safety, the edge of your knowledge of the part of the world that you can't see, but that can kill you. If the canary is in front of you, that is the edge of life leading to death. If it's behind you, you exist in a pocket of safety, bracketed by death.
It's attached in my head to two other images:
1: the glowing pink bricks of Chernobyl. I heard it on an npr radio commentary, talking about after the fallout of Chernobyl when everyone was first dealing with it. During the cleanup people noted these lightly pink glowing bricks. The were actually bricks of carbon that were so irradiated that they were glowing at around 900 degree's farenheit. If you saw them, if you were close enough to see them, you were dead. The radiation output guaranteed you'd die of radiation poisoning of cancer in the next 10 years. It is a very small representation of the vast majority of our universe outside of earth. The sight of them doesn't hurt, it's nothing anyone would think of as dangerous, yet it is the very image of death.
2: the beyond the veil scene in Harry Potter (SPOILERS AHEAD). It sounds silly, but that scene represents one of the most impressive (to me) concepts in literature, much like what I say above. In it, harry and a group of his friends/family are in a fight in the ministry of magics hall of mysteries. They're fighting in a place that has a stone door frame, with a curtain hanging down to cover it. Sirius Black, Harry's uncle, gets stunned from a spell. He's knocked back through the curtain and disappears. Harry wants to go in after him but is held back by everyone else, telling him he's gone. The idea of that, that to harry all it was was a curtain. Sirius had just fallen through it, he was laying 3 feet through the door, all harry had to do was reach in and grab him, but couldn't. Because beyond it was nothing, it was simply death in it's invisible but physical form.... It impresses me greatly.
worth noting that I hate the movies rendition of that scene, they had a floating cloud instead of a physical curtain, and Bella Lestrange throws a killing curse instead of just a 'green spell', which to me was a stunning curse.