Visible crew/equipment: In the scene where she drives the car (with the kidnapped woman in it) down the hill towards the breaker/electrical box, when she hops out at the very last second you can clearly see a person dressed all in black sitting in the driver's seat driving the car down the hill.
Visible crew/equipment: When Robbie takes Sil home, a reflection of a boom mic can be seen on the glass door behind him.
Visible crew/equipment: When the alien is driving off with the guy from the club in his BMW, you can see the entire crew reflected in the passenger side door as it drives by.
Answer: You could probably make a compelling argument that, as an alien-hybrid, Sil is stronger than a normal person and thus was just able to forcibly cut through the finger with the pruners by "crushing" it. Also, this is where good old suspension of disbelief comes in. The pruners might realistically have broken at some point, but it's a movie, so we can "forgive" this bit of unrealism because it creates a compelling scene.
TedStixon