Meaning of "Bell-ath-kweth" in Steve Martin's Picasso at the Lapin Agile?

[Jake B]

In the play, Schmendiman has a line that reads, "Which one's Picasso?... I've heard of you...nice work. If you like blue. Come to think of it, it's about time for a Spaniard again... It's been a long time since "Bell-ath-kweth." I'm just needlin' ye!" What is he referring to when he says "Bell-ath-kweth?" I'm doing this monologue for an audition and cannot find out what that means for the life of me. I've searched all over the internet and found nothing.