I noticed some insects (especially flies) are quick enought to escape
from time to time. Saturday i sat here, together with a friend, and by
random we noticed a green fly to walk inside a large trap. The trap
closed, the fly was caught at the edge of the trap but escaped. Next
trap, a smaller one, was too slow, too. The third one caught the fly,
silly thing.
Another possibility: small insects may escape the closed trap, if they
are small enought. The plant uses this to let insects not worthy the full
closing and opening of the trap to escape.
Ciao, Daniel.