It's October, and Halloween is getting closer, so when I think about D&D I think a little more about horror elements than I usually do.
Scarecrows have been D&D monsters for quite a long time - since the beginning, really. I've only been playing since 3rd edition, but the internet tells me that the scarecrow goes all the way back to the 1e Fiend Folio.The common themes behind all versions of the scarecrow are that it's a form of construct made of straw, and that its purpose is to scare in order to protect something. In real life that something is crops, and the scarecrow is scaring off birds (like crows) by making them think a human is present.
But looking at 4e's scarecrows, they don't really sell the horror for me. I've come up with a different approach that I think makes them much scarier.