It doesn’t really matter, they don’t expect you to get everything right on these. While most of the time you need to get mostly right (Google is using these to train their AI so often they are not sure themselves), they are also looking at other things, like how you move your mouse, and the cookies that they use to spy on people to determine the probability of you being a human. If you pass a certain threshold they let you through, and you can do it even if you miss a square.