Conversation so far:
who did the whistling in for a few dollars more
Alessandro Alessandroni can be heard as the whistler on the soundtrack for Sergio Leone's film, For a Few Dollars More.
Did Alessandro Alessandroni play a musical instrument?
Alessandro Alessandroni played multiple instruments, including the guitar, mandolin, mandolincello, sitar, accordion and piano.

Question: what is the second instrument in the answer
Self-contained rewrite: What is a mandolin?