Thought Sifter

Suspend X+2 — {u}{x}

Whenever you remove a time counter from Thought Sifter while it is suspended, Scry 2.

Whenever a player casts a spell, they may pay {2}; if they do not, put a charge counter on Thought Sifter, and Scry 2.

{p/u}{4}{t}, Remove 7 charge counters from Thought Sifter: Take an extra turn after this one.

The question is, whose thoughts is it sifting?