Just to be a bit picky here: they do not 'know', they have evolved to behave in the way that is most likely to enable their survival.Quote
HOW do newborn mammals know they must seek out the nipple for food?
About 45 years ago, I decided to build, from MFI flat packs, a line of two double and one single wardrobes. When I got it home and unpacked it, I checked all the contents and found, indeed, a something or other missing. I phoned the store and the man I spoke to didn't answer straight away. I said, Are you there? It turned out this was a stunned silence! 'Madam,' he answered, 'in all my years working here, no-one ever checks the contents against the list!!'Quote
Buying flat pack furniture which we know will be hell to assemble and probably have a screw missing...:)
I managed the task and my sons were quite impressed - all they had to do was help me lift the top part to put on top of the wardrobes. And they lasted for 20 years too!