In a book called "What the Dog Saw: And Other Adventures"(https://books.google.co.jp/books?id=6do2AQAAQBAJ&pg=PT77), an exchange between a dog trainer and the dog's ower takes place as below.
"What about the bites?"
"I can see it in the head. She gives me that look."
"She's reminding you who rules the roost."
I have trouble understanding the part "I can see it in the head". Is it an idiomatic expression? (Please see the link above if you need more context.)
Thank you in advance.