10 Small Details You Missed In Dune
5. Paul And Jessica Could Not Be Killed Directly
After Dune is invaded and taken back by the Harkonnens, Paul and Jessica are tied up and brought into an ornithopter to be dumped into the desert. This leaves the audience wondering, if they intend to kill them, why not just get it over with? Shortly after though we hear an explanation from one of the pilots.
The pilot explains to the others that they can not directly kill Paul and Jessica because they may face a truthsayer, a specially trained Bene Gesserit who is able to detect lies based on the tiniest of facial movements and breathing patterns.
Although the attack on Dune was (unofficially) sanctioned by the Emperor, killing these two was off the table. However, House Harkonnen still wanted them dead so they were forced to have them die by other, less direct means so, if ever faced by a truthsayer, they could say "we didn't kill them."
The Harkonnens do not expect them to survive for more than a day in the deep desert, surrounded by sandworms and with no food, water, or stillsuits. Fortunately they are able to escape using the Voice.