No one seems to know . . . certainly not definitively.
Speculations have included
—a slurry for ET’s food
—monitoring nuclear testing residue
—monitoring pollution impacts
. . .
one freaky aspect is that even with people, the people are clearly alive during the procedure—as long as that works out—WITHOUT ANY ANESTHETIC.
Couple that with another puzzle piece . . . that . . . some ET’s reportedly like blood or brain serum or some such from humans WHEN THEY ARE TERRIFIED. That there’s something produced then that’s like a very addictive thrill drug to the ET’s.
I was thinking more along the lines of using the organs as wombs.