'looks like you've solved it'

No errors, mb you need proper indentation.

Your code is wrong. The test is for the string "You're becoming a true freudian expert".
When you code reaches "a", it replaces "a" with "sex". Unfortunately, that means, "freudian" becomes "freudisexn".
Since "freudisexn" doesn't exist in the original sentence.split(), it would never get replaced.
You need to think of some other method to solve the kata.
Also, this is not an issue with kata. So you should mark this as resolved.