A possible explanation is that the long flexible tail of the black rat could be exposed to sticky or frozen substances such as sebum (a secretion from the skin itself), sap, food or excretory products. This mixture acts as a bonding agent and may solidify as they sleep especially when rats live in proximity during winter. Once they realise they are bound, they would struggle and the knot would get tighter. This explanation is plausible given that most cases were found during winter and in confined spaces.[3] Emma Burns, curator of natural science at the Otago Museum, said regarding her museum's specimen, "Ship rats [black rats], according to some theories, are climbing rats, so their tails have… a grasping reflex, In the nest, they form a hold."[4]