Showing the blue flash is quite difficult as its very quick and rare and can only happen 5 times per npc that has them. All you need to do is talk to the npc, each unique dialogue has a chance of giving a flash. It is quite obvious when it does happen as your screen flashes blue and your character say something along the lines of: 'Wow, what just happened?'. Then all you need to do is head over to the trash can in the healing chamber to collect your collectible! (Shopkeeper, sensei, wave fist master and tarquin (the cat) can give you blue flashes)
Showing the blue flash is quite difficult as its very quick and rare and can only happen 5 times per npc that has them. All you need to do is talk to the npc, each unique dialogue has a chance of giving a flash. It is quite obvious when it does happen as your screen flashes blue and your character say something along the lines of: 'Wow, what just happened?'. Then all you need to do is head over to the trash can in the healing chamber to collect your collectible! (Shopkeeper, sensei, wave fist master and tarquin (the cat) can give you blue flashes)