How did I not notice Scarlett Johansson played mermaids at least twice?

I saw The SpongeBob SquarePants Movie in the theaters in 2004 and I saw Hail, Ceasar! in the theaters in 2016 and several times streaming since then.

While watching Hail, Ceasar! last night it suddenly occurred to me Ms. Johansson played a mermaid in both. Now, why is it that my brain never has noticed this before? What is it about the associative connections in my brain that made me notice it on that viewing as opposed to prior viewings?

The brain, or rather my brain, is interesting.