In a statement explaining the recent outages, Bitfinex said that the Ethereum network was experiencing “high congestion” for an unusual reason: “blame the kitties, not us,” the exchange said, rather cryptically.

The kitties, of course, belong to the viral, Ethereum-based game, CryptoKitties. The game, which was developed by AxiomZen, was described by Inc as “a mixture of pokemon and Ethereum”. Players create, take care of, buy, breed, and sell digital kittens that are stored in the Ethereum blockchain.

Join the iFX EXPO Asia and discover your gateway to the Asian Markets

In a way, the kitties function as a sort of cryptocurrency themselves. According to Fortune, each kitty is a “unique, immutable object traded over blockchain.”

The game launched with 100 founder kitties. Each one of the founder kitties could partner with another to produce an offspring with its own unique, 256-bit genome; individual kitties can also sire new kitties that can then be sold to other players. Additionally, the Ethereum blockchain will continue to generate a ‘Gen 0’ kitty every fifteen minutes until November of 2018.

The Gen 0 kitties are sold at prices based on the amount that the last five kitties were sold at, plus an additional fifty percent. The price of a Gen 0 kitty will continue to decline for up to 24 hours, if the kitty remains on the market. Every time a cryptokitty is sold from one user to another, AxiomZen collects a fat 3.75% of the transaction amount.

While the premise may seem a little silly to some, the profits are nothing to laugh at. According to a report from Inc, players have already spent more than $4.5 million on the game. One CryptoKitty sold for more than $117,000; the average kitty will cost you about $90.

Kitties Are Causing Serious Congestion on BTC and ETH Exchanges Right Meow

Despite the fun and games (and potential profits), the CryptoKitties may be causing real issues for Ethereum. The game has become so popular that it is responsible for about 15% of all traffic on the Ethereum network. Fortune reported that this is roughly 8% more popular than EtherDelta, the next-largest smart contract on Ethereum.

According to a report from BitNovosti, reddit users reached out to the developers of CryptoKitties, asking them to pause the game “for some hours” in order to ease the ETH network’s congestion and the high fees that came with it. “There is a huge backlog and it needs to be cleared,” one user wrote.

Is the sudden presence of hundreds of beanie-baby like entities on the Ethereum blockchain a sign of a crypto bubble? Maybe. The appearance of a popular game that was written to operate on the Ethereum blockchain certainly means something, if nothing but a step closer to popular culture. In any case, just like beanie babies and pokemon – someone is making a lot of money off of this.