D&D 5E [5e] Can a Tiny familiar share the same space as its master?

[Sword of Spirit]

These sorts of rules holes reminded me of a funny thing from the core 3e rulebooks. They give a play example that involves a (tiny or small) monstrous spider dropping from the ceiling, landing on a characters shoulder, biting them, and then remaining on their shoulder until the character tries to brush them off.

There isn't any rule I'm aware of in the highly codified 3e that allows that spider to occupy that character's space, and I'm pretty sure it is a direct violation of the rules that do exist.

 

[Tony Vargas]

Anything rules lawyers might come up with regarding 'RAW' in this instance notwithstanding, of course a familiar can share a 'square' (like you should even be using a grid in 5e), with it's master. C'mon, you can't have a raven perched on your shoulder or pet your cat while explaining to the good guy how you're going to kill him like a proper Bond villain? Nonsense.