Advanced Biomedical Engineering
Hypnotic regression of witnesses frequently reveals on-going, repeated abduction extending back several generations. Greys focus on and somehow maintain records of human-family medical histories. (Some witnesses report recognizing the same Grey individuals who abducted them earlier.) Still mysterious nasal implants may support this monitoring program, or they may have another function. The Grey agenda includes genetic engineering, involuntary fertilization to create hybrid fetuses, later removal of these from the human mother, tank incubation in large numbers within the disc UFO, and later presentation of the hybrid offspring to the human mother for emotional nurturing. (Cf. Celtic folklore of human women abducted to nurse stolen human babies and fairy babies.) All of this is supported by a technical infrastructure geared for mass production.
Further reading about alien implants: http://www.alienscalpel.com. See also the book version.