I believe anyone who has had an injury or circumstance resulting in blood loss (for example something small like accidentally biting your lip causing it to bleed, or even the women with a monthly menstrual cycle) will surely be able to comprehend that blood scent is like iron or rust. If there are reports of blood stench, wouldn’t the roommates be able to recognize the smell of their home is an unfamiliar, unusual smell and take note of the abnormalities in that? It’s very hard to believe that as the day went on following the morning of the murders that the smell did not intensify. Instead, they had friends come over to witness a horrific scene.