Dexter told Delilah that she needs to learn how to be a watch cat like him. He spends hours and hours sitting on windowsills keeping watch, but he has noticed that Delilah tends to be a bit timid and if she hears a noise outside, instead of checking on it, she runs and hides in the basement.
Dexter says this is not a good thing and she needs to get a bit braver so he has been giving her Watch Cat lessons. Here you can see him giving her a lesson. Dexter told her she did really well, so well that it is hard to tell which cat is which.