When someone calls you and tells you they are in danger, and you get there about five minutes later and find that she has drowned (or however she was killed), you do NOT cuddle the corpse and do sod all else - you start CPR and keep going until the paramedics arrive.
Similarly, why did nobody try the Heimlich thing etc. on the guy who was attacked at the end?
Other than that, a nice creepy horror / Highlanderish episode and very different from the usual alien invasion thing.
Wonder if Terry Pratchett saw it, and what he thinks of it, given his own work in this field.