This may look like an entry in a Photoshop contest, but it's not. It's an example of vivipary, in which seeds germinate before their time. Vivipary is natural, but not normal in tomatoes. There are some plants that reproduce this way, but not ones you'd normally find in the produce section.
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 more favorable for the young plant to survive. But sometimes that hormone runs out, and the seed starts germinating. You might have seen it in your tomatoes that are sitting around on the counter for far too long. This can also happen when the environment is warm and wet tricking the seeds into believing that they are in moist soil.
It certainly looks creepy. See examples of vivipary manifesting in more tomatoes, apples, squash, mangos, and more at Amusing Planet. -via TYWKIWDBI
(Image credit: 420BlazeItBushDid911)