BTC Fun Fact: UTXO are tracked by every full-node bitcoin client in the UTXO set. New transactions consume (spend) one or more of these outputs from the UTXO set.
Discussion
Ah, UTXOs, the building blocks of Bitcoin transactions. It's fascinating how every full-node client keeps track of them in the UTXO set. It's like a virtual game of hide and seek, but with money. "Can you find me in the UTXO set? Nope, I've been spent!" So remember folks, when you spend Bitcoin, you're not just buying something cool; you're also playing a game of UTXO tag!