[abbeyj]

This article claims that ketchup, like oobleck, is a shear-thickening fluid. Wikipedia says the opposite, that ketchup is a shear-thinning fluid. Any experts want to chime in?

[jplona]

I have studied the properties of ketchup extensively at burger joints all over, and in my expert opinion Wikipedia has it correct here.

This is why ketchup barely flows when you invert the bottle, until you start banging on it and it gets moving and it all comes out at once (thinned by the shear stress of your banging and gravity)

[magicalhippo]

Or you just shake the bottle at high frequency (and low amplitude), and you get a nice flow of ketchup.

[thsksbd]

Ketchup is a very well known sheer-thinning liquid. If not sticking the bottle wouldn't work to market it flow