Have you twigged?

[mnath]

Where does the expression 'twig' come from? For example, 'When I explained to him, he twigged' - as in 'caught on' to what someone is saying. Why use 'twig'?

[Quizmonster]

As long ago as the mid-eighteenth century, the verb 'twig' was used colloquially to mean 'watch/perceive/recognise'. It's easy enough to see, therefore, why it came to mean 'understand' which is just a form of 'recognise/grasp/catch on'.