Icterus is right, it isn't a snake. The curved element draped over the cross is actually a cubist outline of a human figure. It appears to be based on this:
This is Salvador Dali's drawing of the Crucifixion of Christ which he presented as a gift to the prisoners on Rikers Island. All the same, what Francis is holding is a very inappropriate Crucifix. Cubism is not simply another manner in which an artist can approach the theme of Christ's atoning death. The technique fails to contemplate the subject matter in its proper significance and it invariably profanes what is holy. The cubists and surrealists were able to insinuate their profanation into the artistic mainstream without raising the objection of the majority of Christians, because their work induces a quiet, solipsistic, almost Buddhistic mood of reflection which is actually a highly refined form of egotism and very pleasurable to human flesh. It gives one the sensation of being religious without humility or contrition, without acknowledging revealed truth. These, the Resurrexifixes, and other suchlike distortions of the meaning of Christ's death are emblematic of the Cult of Man and proof positive that it now reaches into the Vatican itself.