I can’t work out the instrument Stravinsky uses in "Pulcinella"

Question

I can’t figure out what instrument is being used to aid in keeping his beat. It sounds like pizzicato on the cello, it’s too high for a double bass I think?

You hear it at 1:28 and 2:01 for approximately 10 seconds.

It’s better to hear at 2:01 because the violin doesn’t quite drown it out as much.

Stravinsky in rehearsal

Igor Stravinsky in rehearsal conducting "Scherzino".
In this 1967 program from the Canadian Broadcasting Corporation, he is seen in rehearsal and performance segments, leading The Toronto Symphony in his Suite from the ballet Pulcinella.

Answer 1

Stravinsky uses an unusual division of the strings in this piece. There is a section of five solo strings (two violins, viola, cello and bass), the 'Concertino', as well as the usual tutti string section, the 'Ripieno'.

The two excerpts you mention are slightly different. In the first one the solo second violin, viola and cell are all playing pizzicato eighth notes. In the second one the solo cello is playing pizzicato quarter notes and the solo second violin and the viola are playing offbeat eighth notes.