That's a
very unorthodox style of playing banjo - you can tell they didn't have lot of youtube tutorials back then.
Or maybe Tony thought it was a sitar.
(Or: Given that the song is about the charms of a belly-dancer, maybe he tried to recreate a sitar sound with the banjo because there was no sitar in the studio.)
Speaking of which, here in this live reording two years earlier (still with Graham Nash), Tony Hicks is using something sitar-like to play the song.
The vid Dave posted, here in better quality and with Allan Clarke's announcement,
is from 1969 (a performance in a Scandinavian TV show) and already features Nash's sucessor Terry Sylvester. Nash had left a year before having become estranged from the group serving only the singles market (and his music and lyrics being deemed uncommercial) - with the
The Hollies Sing Dylan project bringing things to a head. There is also another half-live (vocals live with studio backing track) version on youtube from 1968, shortly before Nash left,
where you can hear how much more dominant Nash's falsetto was compared to the (faultless, but less immediately recognizable) one of Sylvester. It automatically reminds me of CSN&Y when he joins in.
And this is The Hollies doing it live 7 years later (of course with Sylvester, I saw them live around that time and they were great) - also with the banjo.
And where is the
Purple connection you cry?! Easy, Ian Paice is a great fan of Hollies drummer Bobby Elliott (and, unusual for a drummer who is often viewed as a more technical player, also of Ringo Starr) and cites him as one of his early influences.