human eyelashes are sometimes used in worm selection or cultivation as they can be more delicate for handling the worm than a traditional platinum wire pick (dog hair can be used as well). However in the above movie, the main purpose of the eyelash was as size reference. (Note: this definition is associated with a C. elegans movie)
An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and perform some of the same function as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object (such as an insect or dust mite) is near the eye (which is then closed reflexively).