Okay, first, instructions:
1. Go to the official Kingdom Rush website.
2. Click on the small bar that says Game Features.
3. Look for the "Tower Abilities" promo image. It is in the top right.
4. Check the right of the group of icons. There is a 19th one that does not match any ability of any tower. It looks like three bloody scratches on a dark brown background. WTF?
Does anyone have any idea what it is, or what it means? Is it a hidden reference to the sequel? Something that was not implemented and for some reason was not removed from the promo? If you know, or have ideas, reply here, because I have been puzzling over it for several days so far.