I bet you, yourself, have seen a sign similar to the ones on this list in the wild at some point in your life. Something so unexpected and funny, you might have even done a double take to make sure your eyes were not deceiving you.

Well, we wanted to learn why that is—why we take notice of certain incongruities or shocking messages in places we did not expect them to be—so, we got in touch with Professor of Psychology at Rutgers University, Maurice J. Elias, who noted that it’s expectations that play a big role when it comes to humor or shock and attention.

In a recent interview with Bored Panda, Prof. Elias explained that a big reason why people find things humorous is that they don't meet their expectations; and they do so in a particular way that brings about surprise and delight.

“This is a key point,” he said. “If I have no expectations, I won't be surprised. That's why so much of humor is topical and contextual.”

“The most enduring humor is about things that change relatively little—marriage, having children, work routines—that are so similar across time and contexts that jokes and humor related to these are transportable,” the psychology professor continued. “Of course, in cultures where these rituals are very prescribed, they won't find things funny that most others might.”

Delving deeper into the significance of signs, especially the funny ones, Prof. Elias suggested that in public, signs can give us an unexpected way of looking at or thinking about something that otherwise was familiar or routine.

Take headlines, for example. “This is not quite an example of amusing signs in public, but I think it's in the same spirit,” the expert noted. Despite being something we see everyday, some of the headlines—especially the shocking or funny ones—can make us focus on them more, sometimes inadvertently. And that can be put to good use! For example, by grabbing the attention of students that otherwise might not be very focused on a certain task.

In a piece for Edutopia, Prof. Elias wrote how using examples of communication errors in news headlines—the so-called bloopers—can help teach students the importance of careful communication.

“In the example, we use poorly formed and often unintentionally funny headlines as a way of getting students to pay closer attention to what they are writing and reading. So in this way, we are using humor to increase attention.”

Arguably, the same method can be used to make sure people pay attention to your sign.

Summing up, Prof. Elias noted that our brains respond well to novelty: funny or shocking things are usually different ‘takes’ on things that are familiar, so they grab our attention. “But as most people know, watching the same shocking thing over and over again loses its shock value and it does not hold our attention as it did the first couple of times. The same goes for things we find funny,” he added. “We stop finding funny things funny and they don't hold our attention.”

So, make sure to stay creative with your signs! What works once, might not work time and again under the same circumstances.