Rainbow was doing the one thing with Spike that he was still able to do, taking a load off and laying on his warm back while he slept. Throughout all the years she had distanced herself from most others, not wanting to have to go through what she had to go through when her family and Scottaloo had left her. Even through all that, Rainbow still held a soft spot for the old Dragon. For a while when he was much younger, there had been a small base on his back. Where once he carried many into battle, now he could barely carry his own head. The years, and the battles they had been through had left him much too old and fragile to do much of anything but keep things warm. Nowadays, even that was starting to become too much for the old lizard.
Rainbow looked around the cave, "How long have you been stuck in here?" She asked the sleeping dragon in a whisper "Two? Three thousand years? And how much longer are you gonna stay? What will happen when you.....NO!" She blurted with a sudden tone shift, "I refuse to think of that, even when.....it finally happens to you. I'll make sure nopony in all of Equestria will ever forget what you have done for this world. Even the littlest thing will be remembered." Rainbow looked at him and sighed "When the dreaded time comes for you to live on in eternal peace, I...no WE will make sure you live on here! Even after all these centuries, we've kept all our friends in our memories, we refuse to forget them! because....because they don't truly leave us until we forget about them!" Rainbow looked down and flinched, during her speech to the sleeping dragon he had awoken and was looking at her. She expected him to say something senile or maybe dopey, what he actually said was nothing even close.
"It’s good to know when I finally pass from this world, I'll still be here, even if it’s only in your heart. It's a nice thing to think when my soon to pass time ends. *yawn* Thanks Rainbow." With his bit said, Spike closed his eyes and fell back to sleep. Rainbow was confused as all hell, but once what he said had fully processed, a look of fear flashed in her eye.
"Wait, soon to pass!?" she leapt off his back and did the only thing she knew about testing a dragons’ health, she flew down, and started a small fire.
Twilight had learned and passed some very specific knowledge on to Rainbow and the others. Twilight found that you could figure out a dragons’ health by simply lighting a fire, and placing it on its back. A dragons’ internal fire, if strong and full of heat, would only absorb a little of it at a time and the flame would slowly die. However if the fire was weak, then it would leech all the heat at once.
Rainbow lit a torch and touched it to Spike’s back. Just as it made contact, it went out. There was a moment of silence. "TWILIGHT!!!" She screamed as she flew out of Spike’s cavern.