Miraculous Effect

The oath was swiftly made into effect once Vanessa realized she could utilize a loophole and nullify the oath later on. 

And of course, Shi Tian was the proud one but remained humble and acted ignorant of the supposed loophole.

To complete the oath was rather simple. There was no need of slicing a finger to drop some blood. That was an old-school thought process and a very inefficient method.

Why must one use their real blood to create an oath? 

The oath was cast with Vanessa manipulating the Magicule in the surroundings and both of them chanted their term one by one. It wasn't simultaneous because who knows if the other party might speak some other words that weren't part of the deal.