Create a function PalindromeQ[str] that returns a value of True if its argument str is a palindrome, that is, if the string str is the same forward and backward. For example, the word refer is a palindrome.

Several dozen words in an English dictionary contain two consecutive double letters: balloon, coffee, succeed, for example. Find all words in the dictionary that contain three consecutive double letters. This puzzle appeared on the Car Talk radio show (CarTalk 2007, June 25).