Board Thread:Theories and Speculation/@comment-5407586-20150624095943/@comment-25079709-20150703105552

Still, Sasuke said that Deidara used the same Earth sign in all of his techniques. Deidara does only 3 things: create bombs, move them and detonate them. So if we know that he use Earth sign in all of his techniques and we know that he doesn't use it to create them or detonate them, the only thing left is their movement. It's really simple
 * He create them with his mouth without any sign
 * He always detonate them with Katsu, NOT Earth sign
 * He move them mostly offscreen.