We found this in our kitchen. It’s very small and appears to be in a casing made of vegetable matter. It's hard to tell how long it is inside the casing, but it's only a couple of millimetres wide. It's not underwater so I don't think it can be a caddisfly.

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Hi Anna,
It looks like the caterpillar of some kind of bagworm moth, although they are usually bigger and found outdoors. That's my best guess.