Hi I'm here to ruin the joke by explaining it. The funny comes from the fact that we EXPECT the old man to be hypnotising her to do dirty stuff, but in reality he is doing so to make her enjoy labour. The humour comes from a subversion of expectation and stark comparison between hypno-r@pe and manual labour as being of similar levels of bad.
Makes more sense than my initial interpretation, that was that he actually raped her, but she was mindbroken and in a world of her own and thought that putting topping on bread was fun while it happened.
"My gift to industry is the genetically engineered worker, or Genejack. Specially designed for labor, the Genejack's muscles and nerves are ideal for his task, and the cerebral cortex has been atrophied so that he can desire nothing except to perform his duties. Tyranny, you say? How can you tyrannize someone who cannot feel pain?"