You can also summon a second Thargoid ship by dropping 5 Thargoid Sensors. Another guy told me that you can do the same thing with 5 Thargoid Probes. I'm guessing if you drop 5 units of any combination of TS, TP, or TL you'll get a second Thargoid.
I dropped Thargoid Resin, Technology Samples, and Biologial Matter and they are not interested in any of those. They do like slaves and imperial slaves (and I think "Master Chefs" but I haven't tested that myself).
you can do same with slaves too. i had a thargoid eating them out of the palm of my hand, and its all cool, those slaves were old stock. Just drop in groups of 5 had one doing its saxaphone routine for about 5 minutes (yes its a saxaphone noise thanks frontier for killing it for me, i actually thought you sourced the sound from a whale or something and then distorted it. But an alto sax really??)