Proper observation of the phenomenon, under scientific scrutiny, occurring naturally with live rats from the start till the end, has yet to happen.[2] However, experts support it being cases of freak accidents with well-observed instances of it occasionally happening to squirrels—also from the rodent family.[5] A 2007 study published in Proceedings of the Estonian Academy of Science, Biology and Ecology, following the finding of the University of Tartu specimen, concluded that the phenomenon is possible but rare.[4]