Commentary for Berakhot 104:12

ולטמא שלחן לאוכלין שבתוכו הכא בשלחן שני עסקינן ואין שני עושה שלישי בחולין אלא ע"י משקין

But the table can defile the food which is upon it ! We deal here with a table [unclean] in the second degree, and [anything unclean in] the second degree cannot make a third [unclean grade] with things non-holy except through the medium of a liquid.

Abraham Cohen Footnotes to the English Translation of Masechet Berakhot