Hello everyone, it is my first post. I want to share what happened to me today. I am working on a project with my Arduino Mega, I wanted to send a string through the serial terminal, I wanted to use this string as a junk flag (Serial.println("start!!!");). And for my surprise, if I placed more than two ginos of admiration when I wanted to upload the program to my arduino, it would get stuck. try it with two signs ("!!"). and the program did go up, but by putting 3 or more signs the bootloader gets stuck. what a surprise. 
:o