We’ve seen Daenerys’ trio of dragons grow from little hatchlings to full-fledged beasts throughout the series, but these fire-breathing reptiles aren’t done growing just yet.

Caution: Spoilers for Game of Thrones Season 7 ahead.

As if Drogon wasn’t terrifying enough as he effortlessly mowed down the Lannister army with his flames in the latest episode of Game of Thrones, he’s expected to get even bigger. Not only do the dragons in the series live for hundreds of years — they also never stop growing. According to the second novel in the series on which the show is based, A Clash of Kings, the largest Targaryen dragon, Balerion, was so big that its wingspan could block sunlight to an entire town.

While animals that never stop growing sound like pure fiction, they do exist in real life. Certain species of fish, amphibians, and reptiles, together with invertebrates like coral and sea sponges, keep growing throughout their lifetime, even after they’ve become mature adults. This is a characteristic that scientists refer to as “indeterminate growth.”

Of course, just because these animals have the capacity to grow bigger and bigger over time, it doesn’t mean they will. Doing so requires infinite resources — both nutrition and space — which are the limiting factor in their growth.

If Daenerys wants to grow her dragons as large as possible, she’s going to have to start feeding them more cooked meat (she found, in Season 2, that they refuse to eat it raw) — whether fish, goats, or, yes, human enemies. According to a 2009 report from researchers from the University of Florida, the bigger the animal, the more food it needs to eat.

In their article in the Proceedings of the National Academy of Sciences, they calculated, using mathematical modeling, just how large dinosaurs were able to grow. They found, unsurprisingly, that larger animals required a lot of food just to stay alive and even more resources on top of that to grow. This led them to conclude that the reason dinosaur size eventually hit a wall was because their access to food sources was ultimately limited. It also shed light on why herbivores were often larger than carnivores: Plants were much more plentiful than meat, which animals had to expend energy to acquire.

Aquatic mammals, the researchers also pointed out, tend to be the biggest because they don’t have to use as much energy to look for food.

The idea that unchecked growth is dependent on infinite resources is also illustrated by farm animals. Pigs, for example, tend to be bigger than their feral counterparts because they are fed regularly and don’t have to waste energy looking for food (Okja, anyone?).

If Dany wants her dragons to reach their true, indeterminately sized potential, her dragons will need to stop flying and fighting and start using all their energy to eat. All the energy they spend in battle could be used for growing, and so the best thing to do is to keep them captive in a massive enclosure and provide them with infinite amounts of cooked protein.

We still don’t know whether the growth of Rhaegal and Viserion has been stunted by being cramped in the catacombs of Meereen, but we did see a much bigger Drogon in the latest episode of Game of Thrones. According to director Matt Shakman, he’s only going to get bigger — specifically, about 231 feet long with a wingspan of 211 feet: In an interview in March, Shakman told Entertainment Weekly that “the dragons this year are the size of 747s.”

Photos via HBO