Where must a tattoo be placed on an animal?

The appropriate placement for a tattoo on an animal is on the inside of the thigh near the abdomen. This location is selected to ensure that the tattoo is discreet and not easily visible to the casual observer, which can help maintain the animal's aesthetic appearance while still allowing for identification purposes. This area also tends to provide sufficient skin surface for tattooing without causing discomfort or interference with the animal’s mobility or daily activities.

In addition, tattooing in this area can facilitate identification and record-keeping for veterinary purposes, as it is a secure and less exposed part of the animal's body. It is worth noting that the other choices do not offer the same level of discretion or practicality for tattooing, making the chosen location ideal for ensuring the animal's identification while inconspicuously marking them.