When two people talk together, they influence each other in subtle ways. The more powerful the interaction, the more powerful the influence. We absorb from one another ways of thinking, speaking, believing, etc. So, in all interactions, we exchange psychological elements. However, when the sexual energy is active, the exchange is more powerful. The more sexual energy is active, and the more prolonged the exchange, the more potent the absorption of psychological elements. The sexual act is a merger of the entirety of oneself, thus the exchange is very deep.

In addition, the exchange is psychological. By "karma" is meant the egoic impulses, tendencies, interests, etc. So, we absorb from others their tastes, interests, tendencies, etc.