It's a good thing that they expect a comeback. With PSG they were "let's give it a try", now they are "yeah, bitch, we are Barca, we can do it". This way the pressure will be on them and if they are unable to score they crumble.
Another thing to consider is that no one was expecting a comeback. PSG players and coach were prepared to defend and go for a goal or two. Now, more and more people expect Barca to put a miracle performance and this could really put an immense pressure on them. This reminds me of the Opium war from 1839-42 when Chinese monks were so deluded that they have supernatural powers, that they tried to hold breath under water for half an hour and try to sink some British ships. As you can suggest - it didn't go well for the monks.
From a psychological point of view the best approach in such a situation is to talk as little as you can and to try to make your opponent complacent. They are doing the opposite of that - I very much appreciate that.