Principally because it's a liquid under ordinary conditions, but shouldn't be. Ever "play" with it chemically? Fun stuff - and toxic. Can evaporate it at one temperature, and re-condense it at a slightly higher temp if conditions are right. It dissolves some other metals - familiar with amalgams?
Chilled some slowly in a liquid nitrogen bath once and grew enormous crystal lattices - hollow shells with well defined edges (roomie was a chemistry grad student back in the day and had access to the entire research lab). Mercury does all kinds of shit that theoretically it shouldn't. You can probably find a YT vid that will do a better job of explaining it.
Looking at that isotope distribution in elemental mercury, it's like it's a hybrid. Might help explain it's weirdness.
I don't know much about chemistry, but something about mercury as always struck me as suspicious and untrustworthy.
Outside of the obvious facts that is has a lustrous liquid-metal allure, and is notorious for being a heavy metal that bio-accumulates and eventually causes madness, or the fact that it was named after the Romanization of the Greek God Hermes...
Something about the fact that it will readily, and greedily, form amalgams with all forms of precious metals, but staunchly rejects iron, reminds me of the old Irish legends, about how Faeries were always rumored to have an aversion to iron.
It strikes me as a metal with malicious and trickster-like qualities, a metal that desperately wants to get into your body somehow.
But that's just me personifying things too much.
You just found a metal jew.