Snake-in-the-grass

We are endowed with a fair share of reptilian wildlife around here. Slow-worms, grass snakes, various kinds of lizards, and adders. Adders like to shelter under rocks, or sun themselves on top. As it happens, I have been working on my dry stone wall recently, and that involves moving a lot of rocks.

Now I don't mind adders in full view, where they are easy to spot. They are shy, and as long as you don't annoy them, they will disappear to safety rather than bite. But I'm not so keen on adders in the undergrowth, because you can't see them, and an adder stepped on is likely to think it's under attack and therefore to respond in kind.

This adder came to my attention yesterday, when I found it under a rock. It's easy enough to see in the first photograph, but it is present in all three pictures, though harder to spot in the other two. How quickly can you find it? That's what I'm worried about.