What's the white stuff that's usually at the bottom of crater wound?

Self protection: When our bodies sustain an injury, the immediate response is inflammation (red, hot, tender swelling). The body increases the blood flow and brings healing factors to the area and also the veins expand to carry bad stuff away. The blood vessels leak and fibrin is deposited in the wound to help clotting and healing. This is what your body secretes to protect the open wound until skin grows.