The Bear's Mouth

"I don't understand. I can't see anything like a bear's mouth. What a strange name!"(p. 18)

What is this phrase about? The students of Bayview High race to get many flags separating green team and red team. They compete the number of flags. Flag is hidden in many places which is difficult to go and find. The goal is "The Bear's Mouth". But what is this?

I thought it was dangerous race because the students face many critical situation. Also I was surprised when I knew Ryan and Gemma are family.
Which team do you cheer?