Did everyone except me know about this?

Sitting in a deli the other day, having lunch, I was battling with the thixotropic brattiness of a new bottle of Heinz ketchup. I’d shaken it vigorously, and was whacking the bottom, to little effect. A girl from a couple of tables away leaned across and gave some advice. Tap on the ’57’ with the side of my hand, she advised sagely. ‘Que?’, I said, falling into Manuel for a moment. Tap on the ’57’ with the side of my hand, she gently insisted. So I tipped the bottle almost directly downwards, held it steady, and then jogged my hand against the label by the neck of the bottle, right where it says ’57’. Sure enough, a steady stream of ketchup emerged, neither too fast nor too slow.

Now, obviously, no matter how runny the stuff is in the bottle, it has to be replaced by air as it comes out, otherwise it’s not going to move. So perhaps where brute-force whacking of the bottom fails to allow a channel for air to move into the bottle, nudging the ketchup to one side of the neck makes such a channel? I notice that the problem has also taxed readers of New Scientist.