What distinctive feature can help differentiate a young rat from a house mouse?

A young rat can be distinguished from a house mouse primarily by its larger head and larger feet relative to its body size. This characteristic is noticeable even in younger specimens, where the proportions remain consistent with the overall differences between the species.

In contrast to the smaller features of a house mouse, the young rat’s larger extremities can make it easier to identify, as they indicate the species' generally more robust structure. This contrast is significant as a mature rat will also have a noticeably larger head and feet, reinforcing the distinction between the two rodents.

Other features, such as a long tail or a flat body, do not serve as accurate identifiers for young specimens, as both young rats and house mice can exhibit a variety of body shapes and tail lengths, complicating differentiation. Thus, focusing on the head and feet size provides a more reliable method for distinguishing between these two types of rodents.