Nick Upton / Flesh fly (Sarcophaga sp.) "bubbling" regurgitated stomach contents in order to increase the concentration of its food by evaporating excessive water content. Wiltshire, UK, September.

Nick Upton / Flesh fly (Sarcophaga sp.) "bubbling" regurgitated stomach contents in order to increase the concentration of its food by evaporating excessive water content. Wiltshire, UK, September.

Ashley Cooper / Ashram's bio-gas plant, that is fed with food waste and manure and fuels the kitchens and the Ashram's vehicles. Muni Seva Ashram,Goraj, near Vadodara, India,

Ashley Cooper / Ashram's bio-gas plant, that is fed with food waste and manure and fuels the kitchens and the Ashram's vehicles. Muni Seva Ashram in Goraj, near Vadodara, India. December 2013.

Ashley Cooper / Ashram's bio-gas plant, that is fed with food waste and manure and fuels the kitchens and the Ashram's vehicles. Muni Seva Ashram in Goraj, near Vadodara, India. December 2013.

Ashley Cooper / Ashram's bio-gas plant, that is fed with food waste and manure and fuels the kitchens and the Ashram's vehicles. Muni Seva Ashram in Goraj, near Vadodara, India. December 2013.

Andy Rouse / Great crested grebe (Podiceps cristatus) feeding feather to chick, aiding digestion, Cardiff, Wales, UK, March.

Markus Varesvuo / Two Black grouse (Tetrao / Lyrurus tetrix) females feeding on little stones to aid food digestion, Suomussalmi, Finland, February.

Markus Varesvuo / Male Black grouse (Tetrao / Lyrurus tetrix) feeding on small stones to aid digestion, Inari, Kiilopaa, Finland, January.

Markus Varesvuo / Male Black grouse (Tetrao / Lyrurus tetrix) feeding on little stones to aid digestion, Suomussalmi, Finland, February.

Anup Shah / Silvered / silver-leaf langur (Trachypithecus cristatus) feeding on the charcoal from a burnt tree trunk to aid digestion. Bako National Park, Sarawak, Borneo, Malaysia.

Nick Upton / Paper wasp (Polistes dominulus) bubbling regurgitated nectar in morning sunshine to speed digestion, Greece, August.