A lot of steak lovers were dumbfounded when they realised that the red liquid on steak is not blood but it is actually a protein called myoglobin.
The protein coincidentally thanks to mother nature appears to be red in colour. Which makes many of us mistake it for blood. The primary function of this protein is to store oxygen.
When exposing to high heat the red turns brown. There is how the cooks determine if your steak gets medium rare or well done. Just imagine cooking without the colour changing we will not know when the steak gets to cook.