SB 10.6.8

vibudhya tāṁ bālaka-mārikā-grahaṁ
 carācarātmā sa nimīlitekṣaṇaḥ
anantam āropayad aṅkam antakaṁ
 yathoragaṁ suptam abuddhi-rajju-dhīḥ
Word for word: 
vibudhya — understanding; tām — her (Pūtanā); bālaka-mārikā-graham — a witch very expert in killing small babies; cara-acara-ātmā — Kṛṣṇa, the all-pervading Supersoul; saḥ — He; nimīlita-īkṣaṇaḥ — closed His eyes; anantam — the Unlimited; āropayat — she placed; aṅkam — on her lap; antakam — for her own annihilation; yathā — as; uragam — a snake; suptam — while sleeping; abuddhi — a person who has no intelligence; rajju-dhīḥ — one who thinks a snake to be a rope.
Translation: 
Lord Śrī Kṛṣṇa, the all-pervading Supersoul, lying on the bed, understood that Pūtanā, a witch who was expert in killing small children, had come to kill Him. Therefore, as if afraid of her, Kṛṣṇa closed His eyes. Thus Pūtanā took upon her lap Him who was to be her own annihilation, just as an unintelligent person places a sleeping snake on his lap, thinking the snake to be a rope.
Purport: 

In this verse there are two perplexities. When Kṛṣṇa saw that Pūtanā had come to kill Him, He thought that since this woman was present with motherly affection, although artificial, He had to offer her a benediction. Therefore He looked at her with a little perplexity and then closed His eyes again. Pūtanā Rākṣasī also was perplexed. She was not intelligent enough to understand that she was taking a sleeping snake on her lap; she thought the snake to be an ordinary rope. The two words antakam and anantam are contradictory. Because of not being intelligent, Pūtanā thought that she could kill her antakam, the source of her annihilation; but because He is ananta, unlimited, no one can kill Him.