You cannot release a sprung bear trap by pressing on the jaws, as Mark and Peter are seen doing with Dawn's leg. Bear traps have springs that slide in and lock the jaws. Even if the trap were constructed in a non-standard manner that allowed this (which would defeat the purpose, as a bear would then also be able to free itself), when Peter lets go of one side, as he is seen doing, the trap would immediately spring shut on Mark's hands in stead of "waiting" for him to release the other jaw.