Dongshan's Each Stitch

KOAN:

Shenshan was mending clothes when Dongshan asked, “What are you doing?”
“Mending,” said Shenshan.
“How is it going?” asked Dongshan.
“One stitch follows another,” said Shenshan.
“We’ve been traveling together for twenty years and you’re still talking like that!” said Dongshan. “How can you be so clueless?”
“How do you mend, then?”
“With each stitch the whole earth is spewing flames,” said Dongshan.