Boa constrictor snakes are in fact far from sweet. Chris is of course being Mr. Sarcastic. However, perhaps the grandmother's visage does resemble that of a boa constrictor. Also, the boa is known for its dexterous prey strategy - to suffocate by tight captivation and then squeeze its prey to death for breakfast. Similarly, the grandmother appears to be suffocating her grandchildren within the confines of a room where they find it hard to breathe.