Excerpt
A chibi's emotions are easy to read-- just look at their facial expressions. Some chibis are happy, others are gurmpy, and some are furious! Just because they're small doesn't mean that they don't have BIG expressions, or even bigger reactions. In fact, chibi expressions are so over-the-top that they are downright hilarious! They react on a much, much bigger scale than regular full-sized characters. It's funny to see huge emotions coming from such tiny characters!
Let's compare the standard expressions of regular-size manga characters with their chibi counterparts. You'll see that the chibi face is distorted and elastic-- stretching way beyond what's normal. The key to chibi expressions is to make them big, broad, and highly exaggerated.