Projection screen was lowered, lights turned off, and a series of multi-coloured dots on many slides were displayed one after another on the screen.

In the dots, there were numbers / letters in colours different from the general background colour of the slide.

Adult: "Can everyone see the number?"

Almost everyone: "YESSSSSS."

One boy: "Ummm - there's no number on the screen!"

Pregnant pause.

One boy: "Oh yeah. Now I see it."

Almost everyone turns their head to look at that one boy.

Test continues.

Afterwards, the one boy was selected for further consultation...