There’s something strange about the pattern of blocks, and Grace is pointing it out to Ada. Although they aren’t looking at the whole complicated machine that produces this pattern of blocks, they can still identify what is unusual. This doesn’t mean anything is wrong, but it tells them that there might be more going on than they first thought.
Forming an idea of what you expect is one way to find patterns. The more you look, the more patterns you will find in nature, in computational artifacts, and in processes. When we recognize a pattern, we can use our other computational thinking skills to help us understand its importance.