During the climbing wall/birthday party scene, Roland and Sebastian are both on their own belay ropes when Roland goes up the wall to get Sebastian. When Roland is lowered to the ground, Sebastian's rope is no longer there.
Wally Mars: Every once in a while, out of all the randomness, something unexpected happens that pushes us all forward. And the truth is, what I'm struggling to think, and what I'm struggling to feel, is that maybe the human race isn't a race at all.
Why didn't Kassie just have sex with Wally or Roland or whomever she wanted to have the baby with?
That would destroy the whole premise of the movie. Kassie didn't intend to use Bateman's sperm and simply just wanted a baby, she didn't want to pimp her body out; not to mention that Roland was already married, so Kassie wouldn't have wanted to commit adultery.She was also using a scientific method which is much more effective than sex. If she simply slept with Roland, pregnancy was not guaranteed. (her method is still not 100% effective, but is much more effective than sex)