What is the fine-grained topic of the following text: In Robert Heinlein's science-fiction novel of 1961, Stranger in a Strange Land, the word is Martian and literally means "to drink" but metaphorically means "to take it all in," to understand fully, or to "be at one with." Only return the topic.
The meaning of "to drink" in Robert Heinlein's Stranger in a Strange Land.