See, there are some air-holes.

You won't stifle." "They are very small--" "How can that be helped?
Who would have doors and windows in a wine-cask?
You will get on board alive, will be released when well to sea, and must not mind a little discomfort." We shook hands, and I stepped in and settled myself as well as I could, with my mouth close to one of the air-holes; and the cask was closed upon me.

The next minute I was rolled slowly off; and a most odd sensation it was! I advise you to try it, if you would like something perfectly new; but have bigger air-holes if you can; and even then let your experiment be short.
I verily believe the porter did his best for me; but how slowly he rolled: and even then what bumps and jolts I had when we came to uneven ground! Now and then he stopped, to wipe his face and rest, seemingly--then on we trundled again Meanwhile I was getting exceedingly hot; all the blood in my body seemed mounting into my head: and unpleasant ideas of smothering obtruded themselves.

The noises around me told me we were on the wharf; then the jolting and bumping became worse than before: I fancied I could tell we passed up a sloping plank and were on shipboard.

Then, without the least warning, I was rolled over and over, and then set upon my head! but a loud cry outside drowned a smothered cry within; and I was placed in a horizontal position again, with feelings impossible to describe.
I think I became sleepy after that; or else in a painless state of insensibility.