What evidence in the excerpt suggests that being a spy for the Americans could be deadly?

The British and the Americans both sent secret messages by horseback riders.
Tallmadge lost some of Washington’s important messages.
TallmadgThe author’s main purpose in this excerpt is to

describe a form of code writing using an example.
explain the mistakes of General Howe during the war.
entertain the reader with a humorous story of miscommunication.
argue that using a mask is the best method for sending secret messages.