"Are not five sparrows sold for two pennies? Yet not one of them is forgotten by God. Indeed, the very hairs of your head are all numbered. Don't be afraid; you are worth more than many sparrows." - Jesus (as recorded in Luke 12:6-8)
In man's treatment of animals, "since they are beings endowed with feeling and sensitive to pain, man is required to ensure that the use of these creatures is never attended by suffering or physical torture." (25) However, animals can and even must be treated as instruments for use/exploitation, "whenever treating them so is the only way of affectively affirming a person or persons." (290, F.4) I can't think of any example other than, if you were driving on a two-lane bridge and there was a large deer blocking both lanes and you had to choose between hitting the deer (very carefully - you know it can be lethal) or driving off the bridge and most likely killing yourself and your passengers, then the obvious choice is to hit the freakin' dear.
JPII writes, "To use means to employ some object of action as a means to an end."(25) If we use a person as a means to an end (i.e. sexual pleasure, landing a job, meeting a cute guy or girl, financial security), then we treat them as an object, making them subordinate to us for our own purposes. Man is free to use inanimate objects, earthly resources, and animals all within good reason to accomplish good ends for humanity. A person, however, by his very nature is to be an end in himself. "To treat one person purely as an instrument 'for the good of' another or even of all other persons is impermissible." (290, F.4) The first example which comes to mind is embryonic stem-cell research. Removing the stem-cells from an embryonic person, actually takes the life of that person, and this is morally wrong, even though many believe that one day these stem-cells will be the most powerful means for creating new human organs or treating diseases in other living human beings.
JPII is all about affirming the dignity of the person; he calls this the "personalistic norm". (290, F.4) A person is "a value not to be compared with anything in the world outside the world of persons." (290. F4)
"For you know that it was not with perishable things such as silver or gold that you were redeemed from the empty way of life handed down to you from your forefathers, but with the precious blood of Christ, a lamb without blemish or defect." - the Apostle Peter, the Church's first Pope, as writen in his encyclical - I Peter 1:18-19