weirdly enough, that effect in biology is electrical
the egg rapidly changes electrical potential after one sperm enters. no more can enter
even weirder, the egg will emit a tiny flash of light (CORRECTION: see @seachanged 's comment below)
it's called a zinc spark
https://www.cbc.ca/news/science/sperm-egg-zinc-sparks-1.3553550

When you meet someone who ignites your passion, it can feel like fireworks are going off. New research by Northwestern University researchers, published in the journal Scientific Reports, shows that when human sperm meets an egg, it can also set off sparks.
Alas, not as luminous as it might at first appear: no light is emitted in-vitro.
From the article, "Upon fertilization, calcium increases and zinc is rapidly released. When this happens, the zinc joins itself to small, light-emitting molecule probes." The word "probe" here is important: it is an introduced chemical that emits the light when it combines with the zinc.
The paper can be read at https://pmc.ncbi.nlm.nih.gov/articles/PMC4845039/
See Fluo-4-AM and FluoZin-3 dyes, within.

Egg activation refers to events required for transition of a gamete into an embryo, including establishment of the polyspermy block, completion of meiosis, entry into mitosis, selective recruitment and degradation of maternal mRNA, and pronuclear ...
Pride goeth before the fall!
Yes, exactly as you say, in-utero and not in in-vitro.
oh
@nixCraft That would be an incredibly immature birth.
Yeah, checks out.
Not the birth, no. 
@nixCraft thanks for the alt-text, as it lead me here thinking it was the original as more recent posts have no alt-text and way worse image quality.
Still I think the original is at https://programmerhumor.io/networking-memes/what-the-hell-is-going-on-zm4i as it has even better image quality.
BTW: I like your "the birth of the internet?" title more than the "what the hell is going on" from my link.