The significant fact is this: No Bene Tleilax female has ever been seen away from the protection of their core planets. (Face Dancer mules who simulate females do not count in this analysis. They cannot be breeders.) The Tleilaxu sequester their females to keep them from our hands. This is our primary deduction. It must also be in the eggs that the Tleilaxu Masters conceal their most essential secrets.
Attributed to: Bene Gesserit
From Chapter 19 of Heretics of Dune by Herbert, Frank