(as) calm as a toad in the sun

What is the origin of the idiom "calm as a toad in the sun" and when to use it?

The idiom "calm as a toad in the sun" originated from rural communities, where farmers and shepherds who often observed local toads sunning themselves in perfect stillness for long stretches with no movement beyond their throat came to use this comparison to describe exceptional calmness. This phrase is employed to highlight any scenario, person, or mood that is very relaxed, peaceful, and undisturbed,