When you look at a picture of three marbles, you don’t have to count them to know that there are three there, your brain just automatically knows that, but you have to count to see whether there are 17 or 18. I remember reading about a study of this for various animals. If I recall correctly, humans can typically recognize 4-5, but can train up to 7 or 8, but crows or possibly an insect have a really high quantity that they can just sense.