InuYasha didn't bother to assess the situation before acting, but with sluggish movements like those, whose to say Sesshomaru would have actually his target? Needless to say, InuYasha's knee-jerk reaction did what it was supposed to do, hinder his god.

The half demon slid back at the force, but not by very far. His teeth gritted as he left out a brief growl. InuYasha pivoted to keep up with the god. Just what was he up to? Another attempt at scent tracking was made, but it was difficult to pinpoint anything in the poison. InuYasha settled with stalking Sesshomaru to his end game, whilst keeping up with him, it occurred to him that it was likely one of the ayakashi. Well that would have explained the reaction.

Using the blood that decorated his hand from the cut caused by catching the blade, InuYasha executed "Blades of blood!" Red jaded, claw-like energy struck out and cut off the creatures escape route. This would allow an opening for Sesshomaru, whether he wanted it or not.