Comic past her prime, Elayne Boosler, attempts to mix poor humor with bad science. Unfortunately for her, it’s old news, the argument in support of abortion isn’t new. It confuses stages of development with ontological identity. However, the real comedy in the tweet comes from her observation being philosophically and biologically correct even though she obliviously mocks her own correctness.
Now, of course anyone ordering chicken in a restaurant would be disappointed if they order chicken and are served a fertilized chicken egg. But only because there is an expectation of a dish containing a butchered mature chicken.
Just like the human being, once the chicken egg is fertilized, it begins its development into maturity. The fertilized egg doesn’t become a human (or chicken), it already is. Rather, it matures and grows.
Fertilized eggs aren’t potential humans, they are potential infants, potential toddlers, potential adolescents, potential teenagers, and potential adults. But it’s a human being the whole way through.
Sifting Reality 
It would have been less funny (not that it was funny) if she concluded with “…and they just give you a dead chick” but the logic would have been the same.
Ive always found it very telling that inthe abortion debate the pro choice crowd is very quick to dismiss science. When they cant deny it any longer, they develop arbitrary loopholes and red tape for the baby to jump through. If those are successfully navigated then nothing trumps “because I want to”.