I think a lot of people have the literal meaning coming into mind, which is mostly why they laugh (unless someone used an idiom in a serious situation). I remember when I done my work experience in a supermarket that was literally a 3-minute walk from my house, the manager there smiled and said, ''so you only live up the road? You could roll in out of bed to get here!'' I never heard that phrase before, but I knew it was an idiom, but I think she must have imagined the literal meaning of that (me literally doing head over hills up the road and all the way into the supermarket) because she laughed and so did I because I thought of the literal meaning aswell. Then I said, ''yeah, it is handy just living up the road.''
People don't use phrases like ''raining cats and dogs'', although I knew what that meant from a very young age. But I've seen other people kind of react to idioms as though they took it the literal way. Like I remember my mum said to my brother, ''can you stop keep jumping down people's throats please?!'' and my brother put his hands out like he was about to dive and went ''whoo-hoo!'' like he was imitating the literal meaning of jumping down a throat. It made some people in the room laugh. When my mum said the idiom, I kind of pictured the literal meaning and my brother must have too, if he decided to imitate it.
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Female