Scientists say the reason you have so much trouble pouring ketchup from the glass bottle is because ketchup is technically not a liquid, but instead a solid. So you need to apply enough force to push the ketchup out.
There are three steps to take to get the ketchup to flow.
1) Shake the ketchup.
2) Turn the bottle upside down and thrust it downward, once.
3) Turn the bottle upright keeping the ketchup near the neck. Remove the cap and tilt the bottle downward at a 45-degree angle with one hand using the other to tap the bottom of the bottle.
And, if all else fails - stick to a plastic squeeze bottle.