But what's really clever about Rio the sea lion is that it hasn't been doing the trick at all between learning it and now.
And marine experts say this proves that sea lions have a better memory than every other animal on earth apart from humans.
Around 10 years ago Rio was taught how to match letters or numbers by rewarding her with fish when she managed to pick out a pair.
Now, without any practice in the years since, Rio has managed to match the pairs again - a skill that experts think helps sea lions recognise different types of prey that only appear at certain times during the year.
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