the.com/grain of salt

means To take something 'with a grain of salt' means to accept it as possibly true but not fully trustworthy, holding back full belief until more evidence shows up.

from The phrase is widely traced to Pliny the Elder's Natural History, where an antidote for poison was to be taken 'with the addition of a grain of salt' — the salt supposedly made the harsh remedy easier to swallow. Whether that origin story is itself fully accurate is debated by etymologists, but by the 17th century the English phrase was already being used figuratively, for claims too dubious to swallow whole without a little seasoning of skepticism.