Ingo Arndt / Mountain gorilla (Gorilla gorilla berengei) yawning, showing stained teeth, Parc des Volcans, Rwanda

Sergey Gorshkov / Snow Goose (Chen caerulescens) pair courting, Wrangel Island, Russia. Sequence 3 of 4

Alex Mustard / 2020VISION / Scuba diver swimming in peat stained waters of River Orchy, Highlands, Scotland, UK. Model released.

Igor Shpilenok / Kamchatka brown bear (Ursus arctos beringianus) at the "Stained glass window" in the Valley of the Geysers, Kronotsky Zapovednik, Kamchatka, Far East Russia

Igor Shpilenok / Kamchatka brown bear (Ursus arctos beringianus) at the 'Stained glass window', Valley of the Geysers, Kronotsky Zapovednik, Kamchatka, Far East Russia

Staffan Widstrand / Hands holding harvested Blueberries {Vaccinium sp} Sweden. Model released.

Flip Nicklin / Bearded Seal (Erignathus barbatus) with head stained red from iron-rich soil sediments in which it forages for food, Svalbard, Norway

Norbert Wu / Humpback Anglerfish (Melanocetus johnsoni) deep sea species cleared and stained for show, bone (Red) and cartilage (Blue)

Norbert Wu / Humpback Anglerfish (Melanocetus johnsoni) deep sea species cleared and stained for show, bone (Red) and cartilage (Blue)

Steven David Miller / Long-billed corella (Cacatua tenuirostris) perched on branch. Ulladulla, New South Wales, Australia.

Duncan Murrell / Lampuyang / Philodendron (Phylodendron sp) growing in the tannin stained water in an artificial canal in the Sabangau (peat-swamp) Forest, Central Kalimantan, Indonesia.

Duncan Murrell / Tannin stained water in an artificial canal in the Sabangau (peat-swamp) Forest, Central Kalimantan, Indonesia.