וְצִוָּה֙ הַכֹּהֵ֔ן וְשָׁחַ֖ט אֶת־הַצִּפּ֣וֹר הָאֶחָ֑ת אֶל־כְּלִי־חֶ֖רֶשׂ עַל־מַ֥יִם חַיִּֽים׃
And the priest shall command to kill one of the birds in an earthen vessel over running water.
Read kabbalistic (mystical) interpretation of Leviticus 14:5: and classical mystical sources.