When dipped in the lava well in a Fortress there are two blinking white Pixels on the screen. See images below.
I'm not 100% positive how to replicate this but I'll put the steps that I did down.
- Go to the Lava Well room in the Nether Fortress
- dip yourself in the lava (Enough so you can still see)
- Look for the blinking Pixels (They are white and sort of obvious if you know what your looking for) (See images below)
It seems that you need to be in lava on fire to see the pixels
It only seems to work in the Nether
It does work in the over world it is just easier to see in the Nether