I found this Southwestern Speckled Rattlesnake out on the surface on a hot day.

The camouflage of this animal doesn’t appear to be working from narrow perspective of the photo, but in greater context, this snake is very difficult to spot. Adjacent hillsides and iron-rich boulders break apart, and this is one of countless reddish blotches against the lighter matrix below. While the snake itself may stand out like a sore thumb, the brain tends to throw it away as noise.

A good read about how our minds tend to do this, even with incredibly important or obvious things:

Gibson, B. S., & Jiang, Y. (1998). Surprise! An unexpected color singleton does not capture attention in visual search. Psychological Science, 9(3), 176–182. https://doi.org/10.1111/1467-9280.00034