Spoiler alert: If you’ve not been to Flat Iron, or Le Relais de Venise, but are going to, and don’t want me to spoil the surprise, stop reading now.

There’s loads of research about how we seem inordinately impressed when we get stuff for free. And I’ve been impressed with how two London steak restaurants have built it into their business models. Oh, and when I say steak restaurants, I mean it: it’s all they do.

First, the slightly posher one: Le Relais de Venise. They serve your steak and chips, and when you’re almost finished, they bring you seconds! Weirdly, sometimes they tell you about it at the beginning, and sometimes they don’t. And even when they do, they tend to say something like the rather cryptic ‘it comes in two services’. Of course, they should never mention it; the surprise makes us all the more excited. Now I’ve been a few times, I’m excited to see the face of whoever I’m with when the waitress comes back round the second time.

At Flat Iron you get a free ice cream when you leave. And they definitely don’t tell you that. What’s more, you claim your ice cream by handing over these cute little miniature steak knives:

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Of course their freebies are built into the price. At Le Relais, their plates are actually quite small. And you’re paying £25. Without the extra helping, you might well actually feel a bit short-changed. But there’s something about the thrill of getting seconds in a proper restaurant that transcends the calculus of ‘total value food consumed’. They’ve sussed that the ‘power of free’ will give us an emotional kick that stops us doing the maths (or doing it, and still feeling grateful).

That’s the behavioural science of steak.