Using the same movie frames, we also measured changes in the diameter of the tongue tip during lapping. Diameter was measured as the distance between the right and left sides of the tongue at the location of the horny papillae. In the early stages of tongue protrusion, the mean diameter was 2.2 ± 0.12 mm and decreased by 27% to a mean diameter of 1.6 ± 0.07 mm in the early phases of tongue retraction. To estimate the volume of the tongue tip at rest and at maximum extension, we modeled the tongue tip as a cylinder. The estimated volume decreased from 18 mm3 at rest to 16 mm3 when elongated (P < 0.0001).
Tongue movements and dynamic shape changes of the tongue tip occur rapidly in G. soricina. The mean duration of a single tongue cycle, from the start of protrusion to the end of retraction, was 0.118 ± 0.002 s (n = 3 animals and 7–31 tongue cycles per animal). The mean duration of the complete feeding bout, including multiple tongue cycles, was 0.33 ± 0.009 s (n = 3 animals and 29 feeding bouts). G. soricina extends and retracts the tongue at a rate of eight cycles per second. Mean time for tongue extension was 0.057 ± 0.001 s (n = 3 animals and 7–31 tongue cycles per animal), and mean time from the start of tongue extension to the appearance of blood in the bases of the papillae was 0.04 ± 0.0002 s.