Apparently a large number of writers have no idea what blood tastes like and it shows. At some point in the last ten years or so there appears to have been a mass decision that the metallic taste in blood is copper. A character gets punched or bites their lip, then notes that the taste of copper to signal to the reader that they are bleeding.
Cool. Except this information is wrong.
What blood tastes like (and smells like to super sniffers like me) is iron. My life experience confirms this. I grew up in Minnesota in the 1970s, when it was apparently a childhood rite to lick railings and flagpoles (especially in the winter). This was not a bloodless activity. In addition, I was a tiny waif (which is hilarious to people who have seen me in person), so doctors diagnosed me with failure to thrive; I had to take liquid iron supplements (which tasted much like liquefied railings). I assure you, that the metallic taste in blood is iron. You might notice a similar taste if you leave something mild flavored (like potatoes) to sit in a cast iron pan long after it’s cooled (the food will absorb noticeable iron).
My grandma had fancy copper cups and copper plated silverware. These had a particular metallic flavor, less bold and biting than iron. It’s not the same taste as pennies, which often smell and taste like oxidizing copper rather than truly copper.
The iron taste (and smell) makes a lot of sense because one third of each red blood cell is hemoglobin, the iron-containing oxygen-transport protein present in red blood cells. It also makes sense that dog blood, which contains 15-20% more hemoglobin by volume, has a stronger iron taste* and smell. I can often tell that a dog is bleeding by smell before I see the injury or blood on the floor (toenail injuries are very messy).
Blood info graphic from Compound Chem.
* I do not go around intentionally consuming dog blood. I have had dogs for years, and this means I have treated a number of toenail injuries and accidental clipping of the quick. I was taught to use styptic powder (or corn starch in a pinch) by dabbing my fingertip on my tongue to acquire powder to then dab on the nail. This is definitely not hygienic and is often gross, but it’s also less messy than trying to press a pinch of powder onto the foot of my squirming canine friends.
S.N.Arly 