Not a dog
Ever since I inadvertently put honeybees in the pre-Columbian southwest (they were a European import) and didn't realize my error until well after the book was in print, I have been an obsessive researcher of the kind of minutiae that, pre-internet, used to make authors throw up their hands and say "I don't care, it sounds logical and I'm putting it in," or scrap that lovely scene that relied on the presence of a piece of honeycomb. Did the Romans have window glass? (yes) Bound books? (only beginning with the late first century) Are marigolds a New World flower? (yes) Fly fishing in the Roman Empire? (only in the late second century)
I have never done anything as truly awful as the guy who thought prairie dogs were dogs and went on for pages about their big feet and floppy ears, but I have nightmares all the same. Even with the wonders of search engines you can spend hours when you are supposed to be writing chasing one fact for a two-sentence appearance in a 400 page book. This is known as verisimilitude, sense of place, and Some Kind of Disorder.
And then there's provenance. Not everyone on the Internet knows what they are talking about, believe it or not. If you are not willing to take the word of the first site you stumble on that Senator Mushrat is actually an alien lizard, then by all means apply that filter to your historical research. There's a lovely Facebook group where I glean a lot of interesting information, but the comments section inevitably bogs down in international squabbles over whose culture was better and thus who built whatever it was, not to mention the ongoing arguments about why Augustus could not have had blond hair (he probably did) and why an iron collar just the right size for a human neck, that says "I belong to Marcus Ginantonicus of the Sixth Legion, I have run away, please return," isn't a slave collar and must have been for a dog.
So much of what is accurate is counterintuitive, and so much that sounds right isn't. And there are so many fascinating things to investigate that aren't critical to your novel and actually fall into the category of Things That Are Interesting But Do Not Belong Here No Matter How Much You Like Them. It's so easy to spend a blissful two hours learning how sewage was disposed of and then realize that you have no place to put it that isn't utterly contrived, and the details are revolting anyway and emphatically not the ambience you are looking for. I have a little folder of these. One of these days someone is going to be appointed Aedile in charge of drains and I will be ready.
Photo credit: Joe Ravi