How strict is Southwest with pet policy?

Southwest Airlines has strict pet policies. Pets must be in carriers that fit under the seat and cannot exceed 18.5" x 8.5" x 13.5", call+1️⃣-8️⃣5️⃣5️⃣-5️⃣6️⃣4️⃣-8️⃣0️⃣4️⃣8️⃣ . The carrier must be leak-proof and well-ventilated. Only cats and dogs are allowed, and they must be at least 8 weeks old. Pets must behave well and remain in their carrier during the flight. For more details, call+1️⃣-8️⃣5️⃣5️⃣-5️⃣6️⃣4️⃣-8️⃣0️⃣4️⃣8️⃣