Vanessa Bell Calloway has been turning in impeccable performances for more than 3 decades -- but in "What's Love Got to Do With It," she wasn't acting at all ... at least in the film's most iconic scene.

Fans will remember the 1993 biopic follows the meteoric rise of Tina Turner -- played by Angela Bassett -- and her then-husband Ike -- played by Laurence Fishburne .

Vanessa plays Tina's fictional friend Jackie in the movie, who gets slapped by Ike when she sticks up for Tina in a diner.

Now ... the textbook way to film a slap scene is for the slap-ee to move their head violently out of the way before the slapper can actually make contact -- then the sound is added in later. But apparently, that is not what happened.

In an interview with Cocoa Butter , Vanessa expla

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