So Kṛṣṇa assumed the nara-hari, nṛsiṁha-rūpa, half-man, half-lion. So these are description in the śāstras.
- rāmādi-mūrtiṣu kalā-niyamena tiṣṭhan
- nānāvatāram akarod bhuvaneṣu kintu
- kṛṣṇaḥ svayaṁ samabhavat paramaḥ pumān yo
- govindam ādi-puruṣaṁ tam...
- (Bs. 5.39)
So there is no significance. This Hiraṇyakaśipu wanted to become immortal. Then, when he was refused by Lord Brahmā that "You cannot become immortal, that is not possible," then, in a roundabout way, he took benediction from Lord Brahmā that he would not die on land, on water, on the sky, no weapon can kill him, no demigod can kill him. In this way, roundabout way, he thought now he has become immortal. So to keep the words of Brahmā as it is, the Lord assumed a form which is not within his description. And instead of killing him with a weapon He killed him by the nails. Nail is not considered as a weapon. So He killed him between day and night, because he also took benediction that "I shall not die during daytime or nighttime." So God, Kṛṣṇa, is so intelligent that we may try to become immortal by so many scientific brain, but there will be some flaw and he wants, must be killed. This is God's intelligence