i have 99 bones on this level but when i try sniffing for the last bone it keeps leading right up to the exit. any ideas anyone?

Did you brake all the plates and all of the bottles? There are some at the begining (plates). Bottles are in the room with Horace and some in the room with the clock and the X. I hope that I helped you. (Did you colect every sticker? I did!)

yea it shureeeeee does

That happened to me in the 1st level. The bones I didn't get was by that bird statue. I had to scare that bird over to the statue.

I can't find the bone either, and I've been searching for two days. I've broken everything I could, and went behind every picture, couch, etc. and STILL can't find the last bone. And like someone said above, you can't sniff it out, it just takes you to the exit. Someone please help me! Is this just a glitch?

Well, you could try sniffing out every single bone from the very beginning of the level. That way, you will be able to collect all the bones before you finish the level, and it won't lead you to the exit. This applies to all the levels, not just the De Vil Manor.