Bella and Edward's relationship is ironic when it comes to strength and skill – she's a klutz with zero muscle power, and he's a smooth-stepping superhero (well, "bad guy" from his perspective). All vampires are much stronger and faster than humans, making them dangerous predators, but some of the Cullens have extra "skills," such as Edward's mind-reading and Alice's ability to see the future. Bella's immunity to Edward's sixth sense makes her all the more interesting and appealing to him. Vampires also have impossibly acute senses, which give them another upper-hand over the human population. But for all their physical advantages, vampires seem to have a harder time controlling their primal urges – mainly, their hankering for human blood. Edward worries about his inner strength constantly, fearing he's not powerful enough when it comes to that force inside him.