This is a key event in The Call of the Wild.

As Thornton got to his feet, Buck seized his mittened hand between his jaws, pressing in with his teeth and releasing slowly, half-reluctantly.

What does this event symbolize?

a shared love for nature and the wild between two pals
a degree of competitiveness between two friends
an air of superiority between two acquaintances
an agreeable handshake between two friends