Adders and humans
Adders are secretive and non-aggressive. They never set out looking for humans to bite, so if you leave them alone, they will do the same for you. They have a highly developed venom injecting mechanism, but will only bite as a last resort. You are very unlikely to be bitten unless you either tread on an adder by mistake or attempt to handle them. Even if bitten, with proper treatment, the worst effects tend to be bruising and nausea, with just ten human deaths from adder bites recorded in the UK in the last 100 years. That said, adder bites are very painful!
Read More: Threats to the adder