  Chameleons are able to capture very large preys by projecting the tongue and
retracting it once it is in contact with preys. A strong adhesion between the
tongue tip and the prey is therefore required during the retraction phase to
ensure a successful capture. To determine the mechanism responsible for this
strong bond, the viscosity of the mucus produced at the chameleon's tongue pad
is measured by using the viscous drag exerted on rolling beads by a thin layer
of mucus. The viscosity of this secretion is found to be about 400 times larger
than the one of human saliva. With a dynamical model for viscous adhesion
describing the motion of the compliant tongue and of the prey during the
retraction phase, the evolution of the maximum prey size with respect to the
chameleon body length is derived. This evolution is successfully compared with
in vivo observations for various chameleon species and shows that the size of
the captured preys is not limited by viscous adhesion thanks to the high mucus
viscosity and the large contact area between the prey and the tongue.
