"I can't tell"

 One of the greatest compliments a player can give me as a DM is to express confusion of a sort. 

Like the session where the party encountered a dungeon room that was a 1970's office full of clerks and secretaries and middle management types, except they were all bugbears. Zak said something like "I can't tell if this originally appeared in the crappy old module or if it is something Jeff added for his own amusement." I'll take credit for the suit-and-tie clad boss bugbear's two-handed sword +1 bearing runes in Old Bugbearese that spell out 'complaint department', but as for the rest? I'll never tell.

Or this week when Bec's PC saw "a crow or something" fly away from the old abandoned church. She was stumped. "I can't tell if that is integral to the plot or if you just made that detail up."

I suspect that the ability to seemlessly move between the module's nonsense and my own personal nonsense is the result of two tendencies:

1. I try to never read aloud from the module. Okay, sometimes I'll read the boxed text that sets up the adventure. And occasionally I will read from the module for comedic effect, such as if it is really poorly written. (Example: I will read aloud dumb mistakes like "32. This chamber is 40' in diameter and perfectly circular, with a chest in the northwest corner.") In general, I'd rather restate the module info in my own words and, if I get things wrong, make my misstatement the reality of the gameworld, then take the words on the page too seriously.
2. I don't take my embellishments to the module that seriously either.