When a player challenges a word and the word is valid, the player who challenged loses their turn.If the word is not valid, the player who was challenged must remove their tiles from the board and lose their chance at placing a word.
Forfeit a turn.
It depends, as long as it is done in each turn then it is allowed.
BOOM
Yes, it can be challenged if the word is actually invalid.
Not in the US or any country that I know of. Dueling is illegal and it matters not who challenged whom.
Johnson
You would have to tell us.
Shah Mohammed Reza Pahlavi
When I challenged the champion I was challenging an ai player named "Matt",
New Zealand, Australia, GB, Venezuela, Switzerland, have all challenged for the Americas Cup
britain and mexico