What's the difference between "lit" used here and "lit" as a slang?
The word "lit" here is used to mean that he moved very fast. The expression "light a fire under" someone or something is used to mean that someone or something moved quickly or was motivated to work harder. Ex: I've never seen her work so hard. Someone must have lit a fire under her. Ex: The runner suddenly had a fire lit under him as soon as the race was about to end. The word "lit" as slang has a completely different meaning. It was originally used to refer to someone who is "drunk", but more recently, it has become another word for "exciting", "fun", or "wild", especially when referring to parties. Ex: She got too lit last night and she is sick this morning. Ex: The party has just started. It's about to get lit!