A Reddit user posted a photo (below) of a well-camouflaged sidewinder rattlesnake hiding next to a door. It blends in so well with the color scheme that it took me a while to spot it.
A person or a dog could have easily stepped on it without seeing it, leading to nasty consequences.
A Wikipedia entry about the sidewinder rattlesnake, recounts a man "bitten on the first joint of the index finger of the right hand, with only a single fang penetrating. Although the bite was described as no more painful than a pin prick, a doctor was seen within about 25 minutes, and 10 cm3 of antivenin were administered. Within 2.5 hours, his entire arm was swollen and the pain was severe, 'as if the arm were soaked in a bucket of boiling oil.'"