Sometimes the DM will announce a situation that requires an instantaneous reaction or response where 'the party' cannot discuss with each other. When the DM announces 'this is a split second decision.'

The player characters cannot speak to each other and the players are not allowed to speak either. The DM will ask each player what their first reaction to the situation is. Once all players have been asked this. Those reactions will occur at the same time. Technically speaking other players are not aware of what other characters are going to do.

Metagaming during these moments could cause your actions to go unresolved.