Replacement for "他一个人" when used in a sentence about an animal

Question

In the sentence:

他一个人在搬东西

Which could be translated as "He is moving it by himself", the important information is 'by himself' (他一个人).

In English we could point to an ant and say "Look, he is moving it by himself". So the sentence can be used for both humans and animals.

What I am trying to find out is the correct way of changing this sentence so it could be used with something that is not a person (人).

Yesterday my son said:

"看，他一个人在搬东西"

When referring to an ant that had decided to carry off a large piece of something and he was impressed that the ant could do it "by himself". But the '一个人' part doesn't seem correct to me since the ant is not a person.

So is the right way to say this:

"看，他一只蚂蚁在搬东西"

Or what is the right way to say this if you don't use '一个人', assuming that is incorrect.

Answer 1

“他一只蚂蚁搬东西” would sound very strange. "他一个人" is natural. I don't know if it's so much anthropomorphism as just treating "一个人" as a fixed expression which acts as an adverb.

Answer 2

An alternative way is to say 它自己在搬东西. but what your son said (he's cute!) feels natural to my ears too. What he used in this sentence is a technique called 拟人手法. :)