What does it mean to send by echo effect?

System: IOS 15.4

Sending by echo effect means sending information by echo. When sound is projected on a large area at a certain distance from the sound source, part of the sound energy is absorbed and the other part is reflected back. If the time interval between the sound directly emitted by the sound source and the sound reflected back exceeds one tenth of a second, the listener can distinguish the two sounds. This reflected sound is called "echo".

Taking iPhone 13 pro as an example, the method of setting the SMS echo effect is as follows: First, open the SMS and enter the text you want to send. Then press and hold the green send button on the right, click on the screen, select the echo effect, and watch the screen special effects. After selection, click the green send case on the right to send it out. There will be a full-screen special effect display after it is sent out.