In many Japanese neighborhoods, you may notice clear water bottles placed outside homes, in gardens, or near doorways and fences. At first glance, this might seem odd—after all, wouldn’t water bottles belong in a refrigerator for drinking? However, in Japan, these water bottles often serve a completely different purpose—and it’s both fascinating and deeply rooted in traditional beliefs and practical needs.
🐱 The Main Reason: Repelling Cats
The most widely believed reason behind this practice is that placing water bottles outdoors is meant to deter stray cats from urinating on walls, fences, plants, or front steps. This practice is commonly known as the “bottle scare technique” or in Japanese, 「ペットボトル猫避け」(Petto botoru neko yoke), which literally translates to “PET bottle cat repellent.”
🔍 How Does It Work?
- The idea is that the sunlight refracting through the clear water bottles creates visual distortions.
- These reflections and flashes of light may confuse or frighten cats, discouraging them from entering or marking territory near the bottles.
- Some also believe cats may see their own distorted reflection in the bottle and avoid the area.
🧪 Is There Scientific Evidence?
While this method is widely practiced, its scientific backing is weak.
📖 What Studies Say:
- A 2006 study conducted by the Japanese Society for the Prevention of Cruelty to Animals (JSPCA) found no strong evidence that placing water bottles effectively deters cats.
- Veterinarians and animal behaviorists suggest that while light refraction may briefly startle a cat, the effect wears off quickly, and cats often learn to ignore the bottles.
✅ Practical Observation:
- In neighborhoods where this method is used, it often becomes more of a cultural or community habit than a proven solution.
🌱 Other Cultural and Practical Uses
Besides deterring cats, some believe that water bottles may serve other purposes—though these are mostly myths or minor practices:
1. Repelling Insects (Myth)
- There’s a belief that water bottles might reflect light in ways that disturb flies or mosquitoes.
- However, scientific evidence is lacking, and pest control experts suggest other more effective methods (e.g., citronella, netting).
2. Fire Prevention Tool (Disputed)
- In rare cases, water bottles have been used in rural areas as makeshift fire extinguishers for small spot fires during dry seasons.
- Ironically, in some conditions, plastic bottles left in direct sunlight have been known to cause fires by acting like a magnifying glass and igniting dry grass.
⚠️ Study Reference:
- Tokyo Fire Department issued a warning in 2015 that water-filled bottles could cause lens-effect fires, especially when placed on balconies with dry materials.
🏘️ Why Not Store Them in the Refrigerator?
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