Angel has flashbacks of his past in the episode Dear Boy. You see during the show in the flashbacks that Angel has been given a soul. Well you see Darla standing somewhere and Angel appears behind her because she left him and now he has found her again. She attacks him and puts a knife to his throat and he wants her to because he can't bear his soul. She moves away and there is a line of blood on his neck. It goes to Darla and then back to Angel and the blood has disappeared.