One of the pets bit the pet sitter while we were away over Christmas (oops...thankfully the sitter is a good friend and wasn't mad!) and as a result there's a splodge of dried-on blood on my living room carpet. The sitter didn't notice it at the time or he'd have cleaned it up but the carpet is quite dark so I can see how he missed it. Not sure how to go about getting it out, any tips?