A: You can use the counter-Surprise function at any time, either during someone else’s turn or your own. Here are some basic examples:

On your own turn:
Someone cancels one of your plays with a Surprise. You play a Surprise to counter their Surprise. Note: although it is your turn, this does not count as one of your Plays.

On someone else’s turn:
They play a Surprise for the in-turn function. You play a Suprise to counter it.

On someone else’s turn:
They play a card. You cancel it with the appropriate Surprise. They counter-Surprise you. You counter-Surprise them!

On someone else’s turn:
Player A plays a card. Player B cancels it with a Surprise. You decide to counter Player B’s Surprise, for whatever reason motivates you.
(In other words, if there is a Surprise/counter-Surprise “battle” going on between two other players, as described in the previous example, you can jump in at any time on either players “side”.)