The hole is actually a dust pit called chiriana and, as everything related to tea ceremony, it has a practical role enhanced by a symbolic meaning. The dust pit is used to collect the fallen leaves and the trimmed twigs. However, while preparing the tea house for guests, the host also places inside the chiriana several green twigs. This indicates the care and attention to detail the hosts puts into preparing the tea ceremony...
EXIF info:
Nikon Df
Lens: 24-70mm F/2.8G
Focal Length: 24mm
Aperture: F/5.6
Shutter Speed: 1/800s
ISO Sensitivity: ISO 500