Usage patterns
〈事〉に落とし穴があるthere is a hidden pitfall in (a plan, contract, etc.)
There's a hidden catch in this contract.
落とし穴にはまるto fall into a (figurative) trap or pitfall
I let my guard down and fell right into the trap.
落とし穴に落ちるto physically fall into a pit-trap
The animal fell into the pitfall trap.
落とし穴を掘るto dig a pitfall trap
They dug a pitfall trap in the forest to catch animals.