Fingernail on chalkboard… the chalkboard can be a tool of learning and connecting to a material with another person who uses one’s hand, palm and fingers that grip a piece of chalk.
Now, if the teacher in this scenario takes a fingernail instead of piece of chalk to the board, the sound normally irritates the common observer, creating a distance between the fingernail person and the pupil in this scenario.
Today, generally speaking, anyone capable of creating a thread online might be that teacher.