You should be feeding your snake a rat that is approx. as big around as the widest part of your snake's body
Not the best advice considering that you do not know the size of the snake in question and no feeding a prey equal the girth size of a snake is not the same as the guideline provided above.

If you had a 4000 grams snakes which I assume you do not have you would based on your advise feed a 300/350 grams rat which is way too big and will only make the animal sluggish and more inconsitant when it comes to feeding.