Drinking from toilet

Why does Pericles want to drink from the toilet?
He gets fresh water in his bowl every morning; sometimes twice a day.

He does have some weird drinking habits. In the morning when
he's let out, he licks dew off the grass. It's rather cute to see.
If I can get organized, I'll take some pictures.

But this toilet bit has me somewhat annoyed. We usually keep
the lid down anyway, for aesthetic reasons, but if we forget, he's in
there!

Anybody else? Any ideas why?

TIA

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Polar