Liǎng rén dōu fàn le tóngyàng de cuò, hùxiāng zhǐzé jiǎnzhí shì guī xiào biē wú wěi.
Both made the same mistake — their mutual finger-pointing is purely the pot and the kettle.
Tips
memory
Tortoises and soft-shelled turtles BOTH have very stubby tails — so the tortoise mocking the 鳖 for being tailless is laughable hypocrisy. Picture two near-identical reptiles, one squinting at the other's barely-there tail.
usage
Common variants: 龟笑鳖无尾 and 乌龟笑鳖无尾. The English equivalent 'pot calling the kettle black' (五十步笑百步 is another close match) captures the meaning, but 龟笑鳖无尾 is more vivid and slightly more colloquial.
