FAQ

Yes she did, although it's possible David picked it up, it seems unlikely as they left fairly quickly to blow the base up.

No it means sport or games. The word freak comes from old english therefore the only latin comparison would be monstrum meaning an evil omen, monster/monstrosity.

lusus -us m. playing , game, sport; dalliance.

Note that "sport" in English also has another meaning, that of mutation, so it is likely that either Dr. Pennington or the screenwriters were misled.

Survival mythology, most cacti are fibrous and you certainly couldn't stick a straw in and drink from it. Even if you found a barrel cacti (genera Ferocactus and Echinocactus) extract enough juice from the inner pulp it can be an unpalatable highly slimy alkaline juice which would cause you to lose more water through vomiting or diarrhea not to mention burning your oro-pharyngeal system. The fishhook barrel cactus (ferocactus wislizenii) with its J-shaped spines may be a possible candidate being the least unpalatable particularly in younger plants; still the above applies chewing small quantities of pith for moisture before discarding - again large amounts can cause vomiting and diarrhea.

I also wouldn't recommend cutting open a cactus just to find out as some species are protected thus it would be illegal to do so.

A ridiculous assertion and blatantly made up urban legend - a hoax! Spiders do not live inside cacti nor make nests in them; just ask Dr. S. Clifford. Again this was another plot device for the film a so called "flashing arrow" or "Chekhov's gun". It is interesting to see that the spiders used in this film were tarantulas which is usually found in the "exploding cactus spider myth". The only thing remotely related by word only are "spider mites" and they are not arachnids.

Now if it were scorpions that could be possible but then there would only be a small solitary one with a dozen or so really small babies - not so exciting.

No he did not - not even close!

Andrew Stevens didn't bother to look up how to pronounce the Latin words correctly; as it is a plot device to make him appear to be a scientist.

Possibly a retractable penis and internal testicles?

David appeared to hope that it would be normal, unfortunately it wasn't the case.

Contrived plot device. Everyone was forgetful, obviously with the whole running out of vaccine and the Lusus attacking the base entrance.

Purely for shits and giggles considering Sharon was doing pretty well with her electric gun in keeping the lusus/human hybrid at bay. Although Von Demming apparently was a masochist and heavily into BDSM - you'll have to ask Andrew Stevens about that.

Most probably.