We can be unconsciously influenced by “salience forcing” making something subtly stand out in out attention (in this case by showing one card for slightly longer).

When this trick was conducted in-person by magicians, it worked 98% of the time, and only 9% of people noticed! 2/2 pic.twitter.com/klXrydImSC

— Ethan Mollick (@emollick) July 31, 2022