Consider - Typing the word consider <mob name here> tells you what your chances are of killing a character. Of course, it's only a rough estimate. Consider compares HP values, telling you if the mob is smaller or larger than you, and levels, telling you if the mob is close to your own level. There is some randomness built in to reflect the inaccuracy of the estimate.
Kill - Typing kill <mob name here> to initiate a fight with a mob.
Example: Kill Zombie