I can't help but add one final thought on the Hethor's slug issue:
If Hethor's slug was in fact Mother Pyrexia, this means that Hethor has the ability to press local fauna (however strange) into service. If this is true, why does Hethor bother with the extra effort (and perhaps, the danger) of summoning creatures from distant stars? There are plenty of dangerous, local creatures already on Urth; why not finish Sev off with one of those?
-- It seems to me that a smilodon or arsinother would have been just as effective against Sev as some of the imports he faces. This to me suggests that Hethor's expertise is limted to the summoning and control of a discrete universe of E.T.s
C/