How can you tell that a rat is freezing? - briefly
A rat that is freezing shows a rigid, immobile posture, pale and cool ears and tail, and a measurable decline in core temperature (e.g., via a rectal thermometer). These signs together indicate the animal is experiencing hypothermia.
How can you tell that a rat is freezing? - in detail
Observing a rodent’s physiological and behavioral responses provides clear indicators of a freezing state. When an animal becomes immobile due to fear or threat, several measurable signs appear.
First, muscle tone increases sharply, causing the body to become rigid. The rat’s limbs remain extended and the posture is straight, without the usual relaxed flexion. This rigidity can be felt by gently restraining the animal and noting resistance to movement.
Second, respiratory patterns change. Breathing becomes shallow and rapid, often accompanied by a brief pause before the next inhalation. The chest wall movement is minimal, and the nostrils may flare slightly.
Third, the eyes exhibit a distinct response. Pupils dilate markedly, and the animal often fixes its gaze on the source of the threat, maintaining a steady, unblinking stare. The eyelids remain open, and the corneal surface may appear glossy.
Fourth, heart rate accelerates. Electrocardiographic monitoring or pulse oximetry will show a sudden increase in beats per minute, sometimes exceeding baseline levels by 30‑50 %.
Fifth, vocalizations cease. A rat that is freezing typically stops emitting ultrasonic calls and audible squeaks, resulting in a silent environment.
A practical checklist for confirming the freezing response:
- Rigid body posture with extended limbs
- Shallow, rapid respiration with minimal chest movement
- Dilated pupils and fixed gaze
- Elevated heart rate (30‑50 % above baseline)
- Absence of vocalizations
Combining these observations yields a reliable assessment of whether the animal is undergoing a freezing reaction. Continuous monitoring of these parameters ensures accurate detection in experimental or clinical settings.