Both players must refer to word judge software, or request an adjudicator if one is unable to do so.
If any of the challenged words is unacceptable, the player removes her/his played tiles and forfeits the turn.
A criticism of double challenge is that it is more conducive to bluffing, although supporters of this rule believe it gives an added Poker-like element of strategy.
A player may play a word he or she knows is invalid in the hope that their opponent will not risk a challenge.
Players are unlikely to challenge a word they know just to gain thinking time, as it may cost points or spread.
Scrabble and Scrabble-like game sites on the Internet such as Yahoo Games' Literati, Internet Scrabble Club and Lexulous offer automatic verification as an option, which makes it impossible to play an invalid word.
The Facebook version of Scrabble and Zynga's mobile game Words With Friends make automatic verification compulsory without imposing a penalty for wrong guesses or a limit on the number of attempts, allowing players to guess repeatedly at words until the computer verifies one to be acceptable.