how the hell did we miss this?...

"Dean could clearly hear wood snapping. Given that the apartment was completely empty except for some shiny new hardwood on the floor, Dean figured it to be the flooring. Wasn't one of Poe's stories about hiding a corpse in the floorboards?
Mackey ran in, and promptly tripped and fell on his face. 
Glancing down, Dean saw that someone had taken the precaution of laying a tripwire a few feet into the front room. 
Sam jumped over the tripwire and into the next room, where the sound was  coming from. 
Or, rather, he tried to. Mackey chose the moment when Sam was jumping over him to try to get up, and his shoulder collided with Sam's long legs. The two of them went down in a tangle of denim and polyester. 
Dean stepped over them both, pistol ready. "Hold it!" he yelled, but he only saw two legs going out the window into the fire escape. The stench of decaying meat made Dean's nostril hairs stand at attention. 
Dean went straight for the window, pausing to turn around for only a second. "Stay that with that jackass!" he said to Sam, pointing at Mackey. Dean also caught sight of several pieces of ripped-up hardwood and bits of wormwood.
He turned and climbed through the window. 
How the hell did we miss this?