Analogies
Analogies
[Megan stands by a TV set and addresses Cueball in the couch and his Cueball-like friend who sits in front of the TV on the floor.] Megan: While I'm up, does anyone want a sandwich? Cueball: Is "sandwich" a metaphor?
[A frame-less panel with the same scene, without the TV. Cueball has taken a hand to his chin and the friend on the floor looks down.] Megan: No, I'm bad at metaphors. But I could try a simile. Cueball: I guess that's like a metaphor. Cueball: Sure.
[While Megan walks past them, Cueball leans forward and his friends looks back up at him as they continue to speak.] Friend: Well, "a simile is like a metaphor" is a simile. Cueball: Is that simile itself a metaphor for something? Friend: Maybe it's a metaphor for analogy.
[Cueball and his friend are still sitting and talking while Megan replies from off-panel.] Cueball: Similes are like metaphors in that they're both analogies. Megan (off-panel): Analogies are like sandwiches in that I'm making one now.

This comic revolves around the similarities (and differences) between the concepts of "analogy", "simile" and "metaphor" (as well as "synecdoche", "sandwich" and "sex.")
When Megan stands up and asks Cueball and his Cueball-like friend if anyone would like a sandwich, she is very literally meaning that she will would go an make a sandwich in the kitchen, and she would make one for either of them if they wished.
Cueball is thus cheeky when he asks if this is a metaphor, because in that case the metaphor would be a reference to sex sandwich , in which case the two Cueball's would make up the bread in the sandwich with Megan as the meat in the middle, in a special kind of threesome (NSFW).
Megan effectively turns him down by saying she is bad at metaphors, thus indirectly saying that she is determined not to understand his innuendo, rather than actually understanding it and having to reply to his smart remark. As she probably also knows him rather well, she also knows that by introducing the similar word simile, she immediately turns the focus off the poor sexual joke to a discussion of language, and she is able to leave the room while the guys are discussing this rather than smirking over the sexual joke.
She also manages to make the punch line after the friend introduces analogy, as she is now actually making a sandwich and using this sentence to make an analogy.
The dictionary defines a " metaphor " as a figure of speech that uses one thing to mean another and makes a comparison between the two. For example, Shakespeare's line, "All the world's a stage," is a metaphor comparing the whole world to a theater stage. Metaphors can be very simple, and they can function as most any part of speech. "The spy shadowed the woman" is a verb metaphor. The spy is not literally her shadow, but he follows her so closely and quietly that he resembles one.
A " simile ", also called an open comparison, is a form of metaphor that compares two different things to create a new meaning. But a simile always uses "like" or "as" within the phrase and the comparison is more explicit than a metaphor. For example, Shakespeare's line could be rewritten as a simile to read: "The world is like a stage." Another simile would be: "The spy was close as a shadow." Both metaphor and simile can be used to enhance writing.
An " analogy " is a bit more complicated. At the most basic level, an analogy shows similarity between things that might seem different — much like an extended metaphor or simile. But analogy isn't just a form of speech. It can be a logical argument: if two things are alike in some ways, they are alike in some other ways as well. Analogy is often used to help provide insight by comparing an unknown subject to one that is more familiar. It can also show a relationship between pairs of things. This form of analogy is often used on standardized tests in the form "A is to B as C is to D".
There is a famously confusing analogy, often falsely attributed to Einstein, that attempts to explain how radio works: "You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat.”
" Synecdoche " (from the title text) is the naming the whole of something by referring to a part, or vice versa. E.g. using "the Internet" when meaning "the World Wide Web", which is only a part of it; or using "Band-Aid" when referring to any adhesive bandage. Randall is saying that he doesn't really understand the difference between them, but instead of using one of the names as a placeholder for them all (that is, as a synecdoche), he actually uses the word 'synecdoche'.  What a mind he has.
[Megan stands by a TV set and addresses Cueball in the couch and his Cueball-like friend who sits in front of the TV on the floor.] Megan: While I'm up, does anyone want a sandwich? Cueball: Is "sandwich" a metaphor?
[A frame-less panel with the same scene, without the TV. Cueball has taken a hand to his chin and the friend on the floor looks down.] Megan: No, I'm bad at metaphors. But I could try a simile. Cueball: I guess that's like a metaphor. Cueball: Sure.
[While Megan walks past them, Cueball leans forward and his friends looks back up at him as they continue to speak.] Friend: Well, "a simile is like a metaphor" is a simile. Cueball: Is that simile itself a metaphor for something? Friend: Maybe it's a metaphor for analogy.
[Cueball and his friend are still sitting and talking while Megan replies from off-panel.] Cueball: Similes are like metaphors in that they're both analogies. Megan (off-panel): Analogies are like sandwiches in that I'm making one now.
