It alludes metaphorically to the individual characteristics and aesthetic appearance of the object. For example, this chashaku is named 'Nomad's Flute', taken from a Rinzai Zen capping phrase in the Shin Zengoshū. The node at the end (Jōō's favoured style) and the pores on one side remind of a flute. The scooping end opens up wide and deep, hungry for cha.
"Oh, the plaint of the nomad's flute is heartbreaking.
Seated guests gaze at each other, tears run like rain."
胡歌一曲斷人腹 koka ikkyoku hito no harawata o tatsu
坐客相看淚如雨 zakyaku aimite namida ame no gotoshi
The whole capping phrase could be used as the poetic name. But from the beautiful scene, 'nomad's flute' stands out to become the abbreviated name. When one informs guests of the poetic name at the end of the tea rite, it would be wise to recite the full capping phrase as well as the abbreviated name and remark how the name was chosen.
If you want to read more about chashaku poetic names and have access to a list created and compiled by Adam Sōmu Wojciński and Sōmu Shachū students for keiko meetings and chaji, choose the option FULL LIBRARY on Adam Sōmu Wojciński Patreon.