The party makes it's way down a corridor. The corridor is well masoned and about ten feet wide. The corridor comes to a four way intersection. To the left and right, the hallway continues for 60 feet and comes to a dead end. A dwarf can detect there is a slight slope in the hall from right to left.
The main corridor continues straight. As the party proceeds straight a trigger is hit and heavy machinery can be heard. Whoever is in the intersection can run across safely just as a ramp lowers from the ceiling in the right corridor and a massive stone column rolls down the hall. It lumbers along, through the intersection and down the left hall where it is lifted up by elevator into the ceiling. The characters can hear it roll back to the right where it re-appears rolling down the ramp. It takes three minutes to roll across and reset itself. The log will continue cycling for an hour.
It is ten feet across the hall. Not a tough problem.
Anyone who walks across the hall must make a reflex save or fall into a foot trap. 12 inch square hole with hinged spikes. The player will take no damage when their foot falls in, but will take damage if they try to yank it out.
I have a three minute egg timer and I put it on the table. The player who's trapped can hear the machine re-set and the log rolling over head. If the log hits him, he's goo.
Easy way out for the player is to push his hands down into the trap and push the spikes down then slowly wiggle his foot out, then carefully slip his hands out.
Once you put the timer on the table and pucker factor kicks in, easy is not so easy.