>>71023235actually the different levels of decay seem to imply it's blood. It has a certain drying speed and viscosity based on size. Furthermore, looking in the top right, we can see the impression of a thumb-print used for the eyes. While that does not imply it's blood, it's still worth noting.
The biggest piece of evidence this is blood is the sticky/viscous nature of the larger globules as compared to the more lightly pressed areas. Notice how it dries in a non-uniform pattern even on the areas without large globs, this seems to imply it's blood and is being "cooled" by the air in a way not common for paint.
How do I know this? It came to me in a dream.