Metal Gear Solid on PS1 originally had Solid Snake befriending rats.
According to a new video by YouTube channel Did You Know Gaming (narrated by David Hayter no less), game director Hideo Kojima wanted to add more rats into the game, allowing the player to assign them names and raise them as pets.
Rats were apparently the first life forms Snake encounters in the cold of Alaska, and would play an important role in the game.
There’s even a reference to this in the Shadow Moses level of Metal Gear Solid 4, where Snake chats to Otacon via Codec about his little, furry friends. This is likely because the rats helped Snake through the vents, but may be a nod to their function as pets too.