Why can indoor cats still react to spring?

Answer: Windows and lamps still change light

Windows and lamps still change light ✓ — Correct! Indoor life reduces some seasonal signals, but it does not erase them. Sunlight still enters through windows, people change lighting and routines, and artificial light can extend perceived day length. That is why an indoor cat can still show seasonal patterns, just less predictably.

Walls leak spring hormones — Wrong. Walls do not leak spring hormones—very convenient for horror movies, not biology. The real point is that the cat's eyes and brain still receive light information, even inside an apartment.

Indoor cats copy outdoor birds — Wrong. Birds can absolutely make a window more exciting, but imitation is not the mechanism. Outdoor birds are a stimulus; daylight and environmental change are the broader seasonal inputs.