Actually it depends more on your skills than the sharpness of the knives. Try it with a empty bottle instead: if your technique is no good, it will just fly off. The trick I dicovered was to utilize your wrist as well right after the knife touched the bottle, and the cut was the same as in the vid. Have fun.
This dude on youtube brought me to this wonder idea to practice with empty bottles instead.
A mind all logic is like a knife all blade. It makes the hand bleed that uses it. - Rabindranath Tagore
PS. Generally a belly or a recurve works best for this kind of practice, however there're always nasty modified (recurved) tanto *cough*EKI CQC15*COUGH* out there who can do the job as well. Use a PE, high quality SE like those on Spydies will just take away the fun.
A mind all logic is like a knife all blade. It makes the hand bleed that uses it. - Rabindranath Tagore
I'm going to have to get some water bottles and try this. Skill is an important factor here so I won't be very good at first. Looks like good fun practice for improving skill.
________________________________________ A Dull knife is always better than a broken knife.