Why would you put things like that on a catwalk? Other than for potential entertainment value? I mean, certainly the models aren't going to be happy about it.
If there were more runway hazards and traps like that, then they might find a new demographic for fashion week. I could be persuaded to watch some some sort of Project Runway/Ninja Warrior collaboration.
I've always pictured models as cripplingly melodramatic - but id probably have the same reaction to finding out I couldn't walk down stairs or avoid slow moving pendulums.