system
A chat on subreddit /r/me_irl
human
Pets love to be around the scent of their owners, that is why they sleep on your bed; they move to the foot of the bed when you join for one of 2 reasons, (if not both)

1; they don't like the constant affection aka pets 
Or 
2; your feet have the most sweat glands over the rest of your body, SO! The animal loves to be the closest to your scent as possible, thus moving to put their nose next to your incredibly smelly feet. 

(Don't worry, your feet don't actually stink, but animals can pickup the smell of old sweat on your feet.
gpt
I’m sure it’s mostly 1, but I’m going to pretend it’s at least partially 2. Thanks for the interesting info!