Using exaggerated gestures to tell a story.

In a lot of cartoons, the story isn't told just with words, but also with exaggerated gestures and facial expressions. Looney Tunes, Tom and Jerry and The Flintstones are all cartoons that demonstrate this perfectly. It's a well known expression that something can be jaw dropping, and in many cartoons, when a character experiences something jaw dropping, the animator over exaggerates the drop. 

Other classic cartoon expressions are the heart literally popping out of the characters chest when they see an attractive character, over exaggerting the anticipation before a character runs off, and eyes popping out of the characters head because they've seen something unbelievable.

These tricks of the trade that are so commonly used in 2D animation, help to easily translate to the viewer what is happening and what that character is feeling, without needing to use any words or add in excess frames that would help tell the story. All the narrative that the viewer needs to know is clearly portrayed in the one character's movements.