It's time for secondary actions
We may be used to seeing the term "multitasking" related to computers, where they are able to run multiple programs at the same time. Something quite similar happens with us all the time, when we're doing more than one action at once.
The animation principle of secondary actions deals with this nature: while we're performing a main action there are a number of complementary secondary actions. For instance, if our character is walking on the sidewalk in a hurry to catch a bus, some possible secondary actions may be looking at his wristwatch—meaning he's probably late—or adjusting his necktie—meaning he was so late when leaving home that he couldn't even properly wear it.
The important thing to notice here is that ...