We are talking about Issa's haiku on haru-koma in World Haiku multimedia.
The key point is concentrated on what is haru-koma
is literally spring hores. It comes from the dance cellebrating New Year.
Just as Lary san said it is a perfomer in Edo era.
The doll above is called [fukusuke, lucky boy] with big head.
He has rid on spring horse.
I think you will undersatnd Issa's haiku by this picture.
the picture comes from the site,