Continuity mistake: After Starbuck's cover as the mechanic is blown, she reaches into her tool box and grabs some guns. She has her hat pulled down over her face, but a second later when she spins around, the hat disappears and is never seen again. (00:26:30)
Revealing mistake: When Billy lies dead in the morgue and the President fixes his hair while saying, "That's better." we can see Billy's throat move as he swallows.
Chosen answer: Her motives are never explained. One possibility would be curiosity, a simple experiment in human infant physiology. Another, perhaps more likely one from her subsequent look of apparent distress is that it was, in an odd way, an act of mercy, giving an innocent baby a swift death, rather than leaving it to die in the nuclear fire or of radiation poisoning afterwards.
Tailkinker ★