Magic ink

 was formed when Kotatsu placed a shard of the Shikon jewel in his ink jar. Although it looked normal at first sight, the ink needed a constant supply of human lives to sustain its life and would attack anyone if it was hungry. Moreover, anything painted with the ink came to life. Also, because of it's mixture of blood and ink, it created a scent strong enough to knock Inuyasha unconscious.

Trivia
Strangely, Shippō, who has a strong sense of smell, was not affected by the scent of the Magic Ink. This may have been because he was not covered in it, or that his sense was not fully developed at the time; Kirara was not affected either.