Mitchell put in the jack of diamonds.

Both shuffled.

Loring cut the pack into two equal parts, using only the extreme tip ends of his fingers, and shoved them together in the same fashion.

Balancing the deck on the open palm of his left hand, he turned the cards carefully with his right thumb and forefinger, keeping up a running fire of comment.
"Now watch me! This trick won't work with any other cards but the jacks.

The reason is easy to see.