Which term refers to small stones ingested by raptors to aid in digestion?

The correct term for small stones ingested by raptors to aid in digestion is "grit," though it seems there was an oversight in this case, as the option provided doesn't represent the commonly accepted terminology. Raptors consume small stones, often referred to as "grit," which help in grinding and breaking down food in their gizzards. This process is essential for their digestion, allowing them to extract necessary nutrients from their prey.

Regarding the choices given, rickets is a condition caused by a deficiency of vitamin D, calcium, or phosphate, affecting bones rather than digestion. Imp refers to a condition involving the feather structure in birds, typically where the feathers do not form properly, and frounce is a disease caused by a parasite affecting birds, often leading to illness. Rangle is not a recognized term in falconry or raptor physiology. Thus, the correct understanding lies in recognizing that raptors utilize grit for digestive function, even though it was not listed among the options.