1) (common)To clap 2 chalk board erasers together to clean them and create a cloud of chalk dust, often fun when students are board.
2) (slang) To clap dem cheeks of the class slut.
1) Hey Tom! Go outsidethe class and clap the erasers!
2) Damn Tom, you really clap the eraser! Dude shes a hoe anyways.
When I went to school in the 30’s, at the end of every day a couple of students were assigned to knock that day’s build up of chalk dust from writing on the blackboard. So, they would go outside and clap two erasers together for a couple of minutes to knock out the chalk dust.
The means by which thoughts are fleeting. The same mechanism that erases dreams works throughout the day, erasing that which the mind doesn't find important.
His dream eraser made it so he exhibited confirmation bias about the situation. He only accepted that which coincided with his beliefs and rejected that which didn't. These people are hard to convince.