Things that go 'thump' in the night..err chimney

Tonight while Jesse and I were sitting at the table eating we hard a loud thump. I didn't really get alarmed because I knew Sally was in the living room and I figured she dropped one of her things. A split second later she came running in the kitchen.."MOMMA! MOMMA! I heard something in the fireplace ... a noise" I could tell she was truly scared. It was all over her face. We went over to the fireplace and looked around to investigate. Couldn't see anything. About a half an hour later we settled in to watch "Survivor". "Thump" there is was again. YIKES!
I think we have a snake in the chimney. We didn't open up the thingy (I don't know what you call it) that shuts off the fireplace from the chimney. Neither of us know anything about chimney's or fireplaces...LOL. Now, my question is this: I ain't lookin' up the thing to see what is in there...LOL! Neither is Jesse. Do you suppose if we ever use the fireplace and open that vent thingy that something will fall out?? There is a screen around the smoke stack(on the outside of the house) to keep critters from getting in, but I really think sneaky snake found his way in. What do I do? I suggested to Jesse he should climb on the roof tomorrow and look down the chimney, but he wasn't too keen on that idea. He suggested that if I was so interested in what is in there, maybe I should be the one. I reminded him how I don't like high places, he reminded me how he doesn't like snakes. Now I really don't know what to do...I am worried that maybe some poor critter is trapped in there. But not worried enough to stick my face in there and look..any suggestions?