Tearing off a head, human or animal, does leave its traces behind.

[All of this is hypothetical, but it's fun to idly imagine, to think about what he would have done, had he been around to investigate those traces.]

But, here we are.

[They are coming up on a low building with metal mesh over its windows and an unfriendly look. Sherlock cheerily raps on the door, then calls inside:]

Mr. Karlsson? It's Sherlock Holmes! I've come to use your facility! I've a fellow monster with me -- open up and let us in!