यदा संहरते चायं कूर्मोऽङ्गानीव सर्वशः। इन्द्रियाणीन्द्रियार्थेभ्यस्तस्य प्रज्ञा प्रतिष्ठिता ॥

yadā sanharate chāyaṁ kūrmo ’ṅgānīva sarvaśhaḥ indriyāṇīndriyārthebhyas tasya prajñā pratiṣhṭhitā

When, again, as a tortoise draws in on all sides its limbs, he withdraws his senses from the objects of sense, then is his understanding well poised.

In plain words: A tortoise can pull its head and legs into its shell. In the same way, a wise person can pull their attention back from the things that tempt the senses. Then their mind is steady.