sentence substitution with ruby using .gsub : Now what if I'm trying to change just parts of a word? Like "Car" to "cah", or vise versa in "Martha" to "Marther". In the second case, if I just did an if like this:

`<if sentance.include? "er"
    user_input.gsub!(/er/, "a")
  end >` 
It would take all "a"'s in "MArthA", which is not what I want.

Any ideas?
For other examples.
http://stackoverflow.com/questions/8381499/replace-words-in-string-ruby/39671330?noredirect=1#comment66644316_39671330