First image and last scene of movie, and Laura's fainting spells

I love this terrific movie and, having viewed it many times, I feel I understand basically all that goes on in it.

However, the very first image in the movie (Rebecca staring at the drop of blood on her finger) and Rene's comment to his and Laura's baby in the very last scene (something like "you're not really hungry, are you?") both draw blanks for me (though the first image is certainly quite striking).

Do these make sense to anyone? (Maybe those having read the novel the movie was adapted from are aware of things in the novel that these two elements of the movie are meant to convey.)

Also, are Laura's two fainting spells (first, when she arrives back at the house very early in the movie, and then again upon exiting the bar after her first encounter with Rene) supposed to make any sense in light of anything else we know about her? Or are they just plot devices plain and simple? (Again, perhaps there's something in the novel that lends these fainting episodes further sense.)