I taste lint in my mouth, then the lights in the place... went!
A cloth filled with chemicals was put in his mouth and he passed out.
Someone snuck up behind Em and put a piece of fabric over his mouth which was soaked in chloroform.
Chloroform is used as an anesthetic which will causes people to pass out.
When he says “the lights went…” he’s referring to the chloroform making him pass out and everything going black, as in “the lights went out”
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