Answer :
The first guess that Think-Tank made about the books found on earth was that they
were sandwiches. He told Captain Omega that they were standing in a refreshment
stand. He also said that sandwiches were the main staple of Earth diet. He then ordered
them to eat one of the books. When Sergeant Oop ate it, he told them that it was not
delicious, and that it was as dry as Martian dust. Then, Think-Tank suggested that the
books were in fact communication sandwiches, and ordered them to listen to them.