Sometimes a seed will begin to develop and germinate while they are still inside their parent, the fruit. The seed first goes through the seed coat and then exits the fruit wall while still attached to the parent plant. This condition is known as viviparous, and it gives the affected fruit a creepy and strange appearance.
Vivipario is a Latin word that means “live birth”, but what actually happens in vivipario is “premature birth”. The seed begins to germinate before maturing and leaving the parental body. This phenomenon occurs frequently in ears of corn, tomatoes, peppers, pears, citrus fruits, and plants that grow in mangrove environments.
Fruits contain a hormone that prevents seeds from germinating. Once the fruit dies or the seeds are removed, the seeds are no longer exposed to these chemicals and can germinate freely. These hormones are necessary to allow the fruit to ripen and fall to the ground where conditions are most favorable for the young plant to survive. But sometimes that hormone runs out and the seed begins to germinate.
You may have seen it in your tomatoes sitting on the counter for too long. This can also happen when the environment is hot and humid by tricking the seeds into thinking they are in moist soil.
The vivipary often shows up as a worm infestation, which is bad if you want to sell your fruits. Otherwise, it is perfectly harmless and does not really affect the quality of the fruit.