Some years ago, there was a discussion - I think it was a private email discussion - about human mutilation cases. There was a consensus that it was virtually impossible to get any information, and that it was covered up even more securely that other UFO-related information. The estimates ranged between 200 and 600 cases over a sixty year period.
When it comes to these mutilation cases, my personal working hypothesis is that there are basically two different types that have an extraterrestrial dimension. The first type would be accidental mutilations in that instead of cattle, people were taken. If the little Greys indeed are programmed bio-robots who can make mistakes, then it is conceivable that they screw up in this way. One of the main reasons I believe this, is because I know of an abductee whose arm was accidentally mutilated by little Greys who screwed up. Taller Ones had to intervene to undo the damage but they weren't entirely successful, and to this day the person has scars.
The second type would be far more sinister and would be intentional. There have been stories about a (very small) group of reptilians who eat human flesh, along with cattle, etc.
This is, without a doubt, one of the most dark and sinister aspects of the alien presence.
It's the work of a minority, but it's real.