Real Question: Why can I smell blood?

This isn't a joke. I really want to know the medical reason behind it. To clear things up... I don't think I can smell it all the time but it's definitely noticeable when someone walks inside from the cold. Especially if they've been exercising... or like working hard.

I smell it really strong on my mom when she comes back inside from gardening early in the morning. One day she was gardening in the front and the back on a cold morning and walking through the house. When I crossed the path she took through the house to get between the front and the back the smell of blood hit me like a brick wall. I could actually follow her path through the house... by smell...

But I can even smell it when people come inside from just standing the cold and not working out. note: I can also smell it on my cat when I let her inside at night. Maybe its iron I'm smelling?? I really just want to know the medical reason... It's the type of thing where I can tell if someone has been outside in the cold recently even if I didn't see them go outside because I can smell their blood. I don't think I;m a vampire or anything stupid like that I'm just curious to know!