The trap are two runes carved on a winged frog demon idol, "kingdom" and "frog." Someone can find these out on an Occultism roll, but reading them triggers the trap regardless of whether the reader has learnt the runes or not, or even tried.
Detect: Per-based Thaumatology, or Perception + Magery for mages, at -6.
Circumvent: Automatic (don't go within 5 yards of the trap).
Evade: Will at +1.
Effects: Any sentient (racial IQ 8+, no Bestial) within 10 yards of the trap who is not a frogman is at -1 to DX and IQ for 1 hour for each point by which he missed the resistance roll.