In the episode 'Lucy Tells The Truth', Lucy makes a bet with Ricky that she will not lie for 100 dollars. Right after the 24 hours starts, Ethel mentions to Lucy a bridge game at Caroline's the next day. Lucy says,'Oh no, no no. I can't spend the afternoon with three women and have to tell the truth. I'll call Caroline and tell her I'm sick.'

Lucy did spend the afternoon with those women and told the truth, so there was the first lie after the bet began. The next lie was her statement that she would call Caroline and tell her she was sick. She did not call Caroline, so the second sentence was also a lie!