Habits PERSON@1 's Possums are rarely seen : they are nocturnal , small -LRB- about NUMBER@1 cm long and about NUMBER@2 grams , or the size of a small rat -RRB- , fast-moving , and occupy the upper story of some of the tallest forests in the world .

They are small , about long and weigh about NUMBER@2 grams , about the size of a small rat .
