As an expert in linguistics and idiomatic expressions, I can explain that the phrase "the fat in the fire" is an idiom that originates from the idea of rendering fat over an open fire to make lard. When the fat is in the fire, it can cause spattering and a mess, leading to trouble or difficulty. In a figurative sense, it means that a situation has been made worse or more complicated, often due to someone's actions.

Here is the explanation with the key term in red:

"The phrase the fat in the fire is used to describe a situation that has become problematic or difficult, typically as a result of someone's actions."

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For example, Now the fat's in the fire��the boss arrived early and will see we haven't even started work. This expression, with its allusion to fat dropping into a fire and causing a burst of flames, was already a proverb in John Heywood's 1546 collection. The American Heritage? Idioms Dictionary.read more >>