SO, my players (40s-50s, professionals all) came upon a line of statues that were going to activate into stone golems in ten seconds if they couldnt guess the next number in a sequence. The magical voice (me) gave the numbers, then started counting down from ten as the statues started to turn their heads at the party. They panicked and babbled until one said ooh theyre prime numbers! and shouted the answer at the 4 count. The constructs stopped moving. Point being, even an easy riddle can be tough if its outta nowhere or live timed somehow. Adds urgency that masks the simplicity of the riddle.