1. Gaps in canon or quetions that canon can't answer - Stuff like my story Of Bracelets is just answering the question of "why does Dean wear bracelets?" Other things are "What made Dean think of talking to Death in order to get Sam's soul back?" ... or "How would Arthur react to being resurrected in a world he's not a prince and everyone is cool with same-sex marriage?" What were those scenes like that we never saw where Sam and Dean carried their brother's dead body back to the car? Or it can be a line in canon, like when Dean threatens to "dream-scape [Sam's] noggin" if he doesn't wake up from his coma soon...well, what would it have been like if Dean HAD?
2. Images - I'll get images stuck in my head and I'll want to write them... I'll want to figure out a story to get me there. Dean with glowing eyes and wings, as Sam accidentally turns him into a patronus when faced with dementors. Tony Stark meeting 1943's Bucky Barnes over a campfire. (I still want to do a longer version of that fic where we see it from Tony's pov - but I'm too intimidated to write Tony pov.) Sherlock in the recurring dream I used to have until my mid-twenties. George Weasley walking down a suburban American street wearing a bowler hat.
3. Sentences/Jokes - With "Sam Is..." I just got the phrase "Sam was catatonic" stuck in my head. "Lies were kept simple" is called that because that sentence was demanding me to write a fic based around it. It just happens sometimes. I'll get a line stuck in my head and my mind won't stop repeating it until I write it down, and only then will my brain be like "okay, now that those words are out, these are the ones that come next..." Othertimes, it will be a joke that I want to make. Vile Violent Vacations is mainly me taking scenes and scenes to set up jokes - I basically wrote 100k words because I wanted to have a punchline somewhere towards the end. I can't even remember what it was now, but I'm fairly positive that that entire fic exists solely for the jokes. I'm actually doing the same currently with the original high-fantasy novel that I'm currently working on. It took me 30k to set up and make my first joke. Now I'm working on setting up the next one. (In fairness though, the fantasy novel is also bunnied by images, not just jokes... also I really love the main character that I've created and I want to introduce them to people.)
4. Prompts - Occasionally, VERY occassionally, I'll be bunnied by someone else's plot bunny in the form of a prompt. This is where Men of Legend came from. Something about someone's idea will trigger a series of images in my head, or make me want to answer a question, or any of the above three things that I listed and I'll need to write that fic.
19 – When you have bunnies, do you sit down and start writing right away, or do you write down the idea for further use?
Neither? I let things rattle around in my brain. I rarely write things down unless I'm actively outlining something that I'm about to write. If I forget an idea... well, if the idea is forgetable then it's probably not very good? Fics rattle around in my brain for days, weeks, months, years... I build on them when I have a moment to stare off into space, or when I'm going to sleep at night.
Now, there are exceptions to this - if I'm bunnied by a sentence that my brain won't stop repeating, that gets annoying FAST and I know I'll get relief if I write it down, so those fics tend to get written sooner rather than later - usually within a day or two of the arrival of the sentence. If I'm bunnied by an image, I tend to sit on those the longest - I like holding images in my brain where they are perfect and in full technocolour glory - and not ruined by my feeble attempts at describing them using my rudimentary knowledge of the english language.
20 – Do you ever get bunnied from other people's stories or art in the same fandom?
Jaein? I get bunnied by other people's stories, but not necessarily in a good way... some of my stories are actually in response to me not liking other people's stories. If you want something done right, do it yourself! So, yeah. It's a really arrogant thing, which is why I'm loath to admit to it.
I don't tend to get bunnied by art at all. It's more like the oppposite - if I weren't so out of practice with art, I'd probably get art-bunnied by stories. Like I said, images are where a lot of my fic ideas come from, and that's me trying to do "art", trying to show you the image that I have in my brain...so, if I could actually do art, then I would draw it. But, yeah, I haven't really picked up pencil/ink/paint, since I was a teen, so I'm HORRIBLY out of practice... words are all I have. I guess that's the difference - I write to convey images, so when I see art, well, it's art - it doesn't need words, it's conveying an image all on it's own.