Mike and Dave like to play Scrabble. Mike never cheats. He always plays valid words and never plays out of turn. Dave, however, cheats. Sometimes he plays invalid words, but Mike never challenges. Sometimes he makes two plays in one turn. Mike never notices. Today, Mike and Dave have started playing a game. Mike played first. After 7 plays, the board looked like this:
As usual, Dave has already cheated one time. How has Dave cheated?