Aunt Betsey scared the pregnant Clara Copperfield. Describe the incident briefly.

In chapter 1 of David Copperfield the title character narrates the tale of how he came into the world. One windy Friday in March, David's mother Clara was sitting by the fire, still grieving over the loss of her husband. Inside her was her unborn child, who, of course, was David himself. As she broods unhappily on her fate and that of the child who'll grow up without a father, she suddenly notices a strange woman walking up the garden path. It's none other than David's great-aunt, Miss Betsey Trotwood.
Betsey is a rather eccentric lady, to put it mildly, with somewhat unconventional habits. Instead of ringing the doorbell, as most normal people would do, she presses her face hard against the window. This would be a pretty scary sight for most people, let alone a delicate, nervous woman in the advanced stages of pregnancy. So as we can imagine, Clara is rather spooked by the sight of Betsey's flat, white face as it presses up against the window pane. David is convinced that the experience gave his mother such a turn that it caused her to give birth to him prematurely.