Remove the bug. flytraps need LIVE insects. And there is no need to feed it. The trigger hairs inside the trap have to be tickled TWICE for the plant to close tightly and secrete it's juices.

What happened is that you dropped a dead bug. The bug did trigger the trap to close over it but it didn't do anything else to indicate to the trap it caught something. It is the stimuli of the bug moving inside the trap that educes the trap. to go into the the digestive phase.

When the bugs moves inside the closed trap, it keeps on brushing against the trigger hair. The trigger hair isn't just only the cause the trap to close. It also send single to the trap that it had captured a live digestible prey.

That's what allows a trap to distinguish between a live nutritious prey from inanimate debris. That way the trap doesn't expand needlessly digesting debris with no nutritional value.

That's why your trapped opened again, there was no further stimuli from the dead bugs because they weren't moving, so the trap had no reason to stay close & digest it. It opened up again.