少了一頭驢 The Missing Donkey

小小趕著十頭驢，他一邊走，一邊數：Xiao-xiao was driving a herd of donkeys.  While walking, he counted them:

一二三四五六七八九十。“On, two, three, four, five, six, seven, eight, nine, and ten.”

小小走累了，他騎上一頭驢。小小數Xiao-xiao was too tired to walk, so he got on one of the donkeys and counted again,

一二三四五六七八九—-One, two, three, four, five, six, seven, eight, nine—-
哎呀！不好了！少了一頭驢。“Oh-no! A donkey is missing.”

小小急得跳下來，他又數：Xiao-xiao panicked and jumped off the donkey.  He then counted again:

一二三四五六七八九 十。嗯！沒錯！Hmm,  It’s correct, he said.

小小騎上驢，他再數：Xiao-xiao got on the donkey’s back again.  He counted one last time.

二三四五六七八九—One, two, three, four, five, six, seven, eight, nine—-

哎呀！怎麽又少了一頭？“Oh-no! A donkey is missing again.”

這是怎麽一回事兒？What on earth is going on?