Problem:
Many animals have red tongues, though not all of them - blue-tongued skinks and giraffes come to mind.
Question: Are they red because of the blood (and therefore hemoglobin) in them? Please justify answer.
It sounds plausible, but it also sounds like a post-hoc explanation.
I'd be especially curious about any other species having blue blood, like horseshoe crabs, but still having red tongues, unlike horseshoe crabs, which apparently don't even have tongues.