Players can say anything they want to each other. They can collude, make threats, spread disinformation, speculate about roles, tell others what they know, and lie about what they know.
Other than as instructed, players may not physically reveal any role card to another player for any reason before the game ends. You can say what you want, you just aren’t allowed to prove it.
Revealing Cards When Playing Them
When playing a card from their hand, a player is allowed to play a card face-up that they would otherwise be entitled to play face-down.