"Roll Call" joke

It was early morning at the military base, and the first sergeant was calling out names for the daily work parties listed on a piece of paper: "Jhonson"
"Here!"
"Joe"
"Here!"
"John"
"Here!"
"Michael"
"Here!"
"Seeback"
No answer.
"Seeback!"
No answer was heard again.
"SEEBACK!!!"
The troops remained totally silent.
At that point, someone whispered into the first sergeant's ear. He looked again at what the last name really said, turned a bright crimson red, and quickly turned over the list to continue calling the names printed on the other side.