Watch the top two cards, not your stack
Every pattern is decided by the card that just landed and the one or two beneath it. Name each card in your head as it lands ("nine… nine!") and keep your eyes on the pile even on your own turn. With Classic rules a pattern lands about once every 12 flips; with Extended rules about once every 7, so the extra rules mostly reward attention.
Slap the card, not the hope
Pressing as a 9 is about to land on a 9 is a guess, and the table treats any slap under 0.12 seconds after the card as too early: it burns. The near misses are the trap: a 6 then a 7, or 7, King, 8, look like patterns for a split second. A slap you miss costs nothing, even if it lands a second late; a slap at nothing costs a card. When in doubt, wait for the card.
Speed you need at each level
Easy reacts in 0.6 to 0.9 seconds, Standard in 0.33 to 0.48, and Expert in 0.24 to 0.32 after the card is visible. Missed reactions take longer. In 100,000 seeded reaction races, a 0.4-second slap beat one Standard computer about 57% of the time and three Standard computers about 18%. The computers wait for the same card flight you see, so animations on or off use the same reaction bands.
Challenges: keep watching the pile
When you are answering a King with three chances, your flips are also new chances for a pattern, and a slap takes the pile from the challenger. When you are the challenger, the pile is not yours until it is taken: the last flip can make a double that someone else slaps first.
At zero cards, slap only what you are sure of
With no cards you cannot burn, so a false slap puts you out. A sure double is your way back in; a guess ends your game.
What the numbers say
In 30 simulated games per table between evenly matched Standard computers at Normal speed, two players needed about 320 flips (five minutes) and four players about 1,350 flips (21 minutes). Extended slaps made four-player games longer: about 38 minutes. A stronger slapper can finish much sooner. In 30 four-player games per level against three Standard computers, Easy won none, Standard won six and Expert won all 30. A simulated player reacting 250 to 500 milliseconds after the card was visible won about 64% of slaps against one Standard computer and about 11% against one Expert computer.
12-second floor and the short claim window limit.