The BBC reports on an aggressive Muntjac deer that's been attacking dogs at Ampthill Park in Bedforshire. I've seen a few Muntjac in the wild, but usually just the rear end departing swiftly into the bushes, so I haven't had a good view of the sharp bits at the front, but Muntjac are quite fearsomely endowed with small sharp horns and long curved canine teeth akin to tusks.

They're only as big as a medium sized dog and run scared at most things, so I imagine this aggressive individual may be protecting its ground or being taken by surprise at close quarters. Or maybe it's just plain aggressive. It's easy to forget as we study the identification books that animals don't all conform neatly to the given descriptions and can be as varied in physical and behavioural traits as humans.