It took quire a while for her to get to that point. Now if I scritch her, she never seems to get enough.

She has a certain look on her face, and will sometimes just stick her head in my hand when she's not done. For the most part though, she's pretty gentle about asking.
Alex on the other hand is very pushy about scritches, to the point where I can't have him and Lucy next to one another when I'm trying to pet either one of them. Alex gets pretty jealous, and will try to chase Lucy off. Lucy, being as stubborn as she is, usually won't budge, and will actually try to fight back. So things can get pretty crazy at times.
Funny enough, Lucy will lower her head when asking for scritches, whereas Alex just puts his entire head in my hand. He's very demanding like that.

He also knows that "kisses" will get him scritches, and so he will give me a small peck on the lips for them.