The Beads of Subjugation are the beads around InuYasha's neck. They are activated when Kagome says "Sit!". Kagome is the only person who can activate the Beads of Subjugation, as Kaede intended them for Kagome's use when she first put them around InuYasha's neck. The force of the spell is so great that upon activation InuYasha plunges face first into the ground. Although originally made by Kikyo for this purpose (with the phrase "beloved" instead of "sit"), she decided against giving it to InuYasha and never used it.
The Kotodama no Nenju is introduced in the very first manga as a spiritual device to control InuYasha. It was originally intended to keep InuYasha from killing or hurting Kagome. It is not used often anymore due to change in InuYasha's personality and is only used as comic relief, to save his life, or to reverse his demonic transformation.
It consists of a number of round beads and a few magatama which are often mistaken as claws. The magatama is an ancient comma-shaped bead imbued with great spiritual and mystical powers.