There is an actual condition called the Tetris effect

There is an actual condition called the Tetris effect. It makes you see the Tetris shapes WHEN YOU'RE NOT PLAYING THE GAME

People who devote a sufficient amount of time and attention with routine Tetris playing may begin to start seeing Tetris shapes and movements as a form of either habit or Hallucination in the corner of their eye or when falling asleep. You may perceive Tetris shapes that aren't there, or think of flipping around real-life objects as if they are Tetris shapes.

They tested the Tetris effect on people with amnesia. Amnesic patients played Tetris for extended periods of time, and even though they later had no recollection of playing the game, they still had dreams about Tetris in their sleep!

Tetris has also been used on patients with Post-Traumatic Stress Disorder too. In studies, extended Tetris play helped diminish the number of traumatic flashbacks in patients.

There hasn't been a reported case of smallpox since 1978.

Smallpox is a deadly disease that used to be very widespread. It would kill 1 in 4 people that were infected. Most of the survivors of smallpox would be blind or scarred. In the 1950s there were 50 million cases of smallpox every year.

The World Health Organization intensified the effort to eradicate smallpox in 1967. The eradication effort worked! The last case of smallpox occurred in a laboratory in the United Kingdom in 1978. Before that, the last natural case of smallpox was in Somalia in 1977..