What is the main idea in this picture?
1. The lake
2. The bridge
3. The alien

I would say Alien

Explanation:

I don't really know if there's more to the picture meaning like a book or a passage. But I think it's the alien. The bridge and lake are normal. However, the alien is something one may never see. Maybe the picture is trying to say that amongst our normal, there is something off or unusual.

Hope this Helps!

the answer of "what has three legs but never walks" is a yard stick. this answer can be found at