When my oldest son was a toddler, I gave him a bottle (baby bottle, when still drank out of those) of milk when we were at my mother's house for the night. It was a bigger bottle, like the 9 oz kind. Filled up the thing. He took it and toddled off. Shortly after that, we looked for the bottle and couldn't find it. Looked all over, and could NOT find it.
He's 14 now, and we NEVER found that bottle.
And I asked my mother later that week if she found the bottle. Nope, she never did. And yes, we checked the garbage. I thought for sure we'd find it at some point, because hey, it was milk, and it would obviously start smelling pretty soon if it was left out. But no, we never found it. My mother has since passed away, and we cleaned out her house to sell it. Never found that bottle. And it still bugs me.