When the toilet looks like it's not going to flush, but suddenly lets go at the last minute. Happens especially when you start digging for the plunger. Ususally a pleasant surprise (especially when in a strange bathroom with no plunger).
Guy triumphantly emerging from bathroom: "Flush fake-out! I thought I was going to have to wrestle that turd down the toilet, but just as I reached for the plunger it let go all on its own."