Shrikes kill with the bill, using a hooked upper mandible with a tooth-like projection that can sever the neck vertebrae of small vertebrates. What they cannot do is pin a carcass down: their feet are ordinary songbird feet, without the strength or curvature of a hawk's talons. Wedging or impaling the body on a thorn, a twig fork or a wire barb provides the anchor point instead.
The habit also serves as storage. A larder of impaled insects, lizards and small rodents can be revisited over days, which buffers the bird against poor hunting weather. In some Lanius species, the size of the larder appears to function additionally as a display to females.
The common misreading is that impaling is a cruelty or a trophy behaviour. It is a mechanical solution to a handling problem, and the same species will simply hold small soft prey in the bill without impaling it at all when the item is easy to manage.