Fido is the quiet, thoughtful one. When Gnasher shakes herself off after a lava-swim and accidentally immolates a Black Knight, she watches, licking her lips. She encourages Gnasher to enjoy some zoomies, pointing her at Zamorakian magi and bookcases full of explosive tomes. As Gnasher twitches in a dream, Fido is whispering in her ear.
You have to watch out for Fido. She is biding her time for something.