Several methods were used. The most popular was hitting the bottom of the bottle. The trick to this is not keeping the bottle straight but on an angle.
Another method used is to gently tap the sides of the bottle, while it is of course on its side and slightly tipped up. As demonstrated in the photo above.
If you put the lid on the bottle and grip it at its base. Then swing your arm as if you were throwing a ball overarm. This method forces the ketchup to the top of the bottle, allowing you to pour it out. Remember put the lid on the bottle, it’s important. One of my kids used this method once with a bottle of mustard and it was all over the carpet because the lid was not on properly. So use with caution, I am not responsible for damages. Did I mention that mustard stains?
To get the ketchup flowing evenly heat up the bottle for a few seconds. Remove he lid and place in the microwave for 10 seconds. This will allow the ketchup to heat up and thin out a bit.
Take a long thin object – like chop sticks. Place it in the bottle and stir, this mixes up the sauce and allows it to flow free.
Lastly, all you really need to do is squeeze the bottle.