Hi, teachers.

What does the following phrase mean? "burrs on its trousers"
The full sentence id:
"Confucius: Though deeply revered, Confucius has mostly managed to avoid being turned into a god. But that didnít prevent his practical, secular philosophy from gathering plenty of supernatural and superstitious elements, like burrs on its trousers, as it hiked forward into the Middle Ages."

It come from "Atheist for dummies."

Thank you in advance.