Allow me to explain, celestial bodies are not flat, two dimensional disks. Imagine that when two planets are lined up there is a 'magnetic' bond. Now thrown in Elenin piercing through that bond an resulting in cavitation like a bullet.

Or, when the Earth is sandwiched, between Elenin and another celestial body, Elenin disrupts that bond, pulling against the bond.

Many people misunderstand, that is not just the mass of the object, it's the object's velocity, and internal structure that create its effect on other bodies.

See, people that keep comparing this thing to a flea on an elephant don't think about the fact the flea can still affect the elephant.