My humble answer is : You don't.
Let's say you came back home and found that someone created a mess, a havoc in your kitchen.
And your cat looks so innocent that you just can't believe it did it.
The door was closed and on security, so you know it wasn't opened.
The only possible hypotheses explaining the state of your kitchen is that something get there through the cat flap and did it.
You can't possible know if it was another cat, raccoon or squirrel.
But you absolutely sure that, whatever it was, it must be something being able to sneak through the cat flap.
So we know something for sure about that potential perpetrator: it is small enough to fit into the cat flap.
I wouldn't argue with you on that.
I probably would argue with you about why you are so sure your own cat didn't do it.
I hope it explain why we shouldn't argue with the 'God is infinite' statement, the God that is not infinite just won't fit into a cat flap.
Please excuse my English, I am still working on it.