Sawyer claimed to have heard a frog whose croak was so loud it prevented him from sleeping and drove him on a quest for vengeance. It is unknown if Sawyer actually heard the frog or not, as Jin was passing by at the time and made no indication that he could hear it. On his mission to seek revenge against his tormentor, Sawyer encountered Hurley who had important knowledge of the frog's whereabouts. While still looking for the frog, in a rare moment of emotional vulnerability, Sawyer reaches out to Hurley for help. Eventually, they found the frog and Hurley pleaded with Sawyer to spare its life. Instead, Sawyer crushed the frog to death in his hand. Sawyer then joked about eating the frog with ranch, a cruel reference to Hurley's stash of food seen earlier in the episode. ("One of Them")
The frog was a symbol of fertility to the ancient Egyptians. In Egyptian mythology, there is a frog-headed goddess named Heqet, meaning "frog". In addition to fertility, she was also closely associated with resurrection. Rebirth, both the literal and figurative sense, is a major theme of Lost.
Although the characters refer to the frog as a "tree frog", which are members of the Hylidae family, the actual species of the frog is Dendrobates auratus, which is a member of the Dendrobatidae family (i.e., poison dart frogs). They are native to Central America but were introduced to Hawaii, where Lost is filmed, as means of controlling the mosquito population.
Sawyer's killing of the tree frog contrasts with his earlier encounter with the wild boar. After he caught up to the boar that had been tormenting him, he unexpectedly spared its life, contrary to his original plan. ("Outlaws")(Juxtaposition)
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