Sound Vs. Leaf: 111 :

The introduction of the "State 2" Curse Mark process.

Sasuke officially begins his transition to the "second state" of the Curse Mark by consuming the Mind Awakening Pill. To survive the process, the Sound Four seal him inside a barrel for safe transport. 111 : Sound vs. Leaf

For more details on the episode's plot, you can check the Narutopedia entry . The introduction of the "State 2" Curse Mark process