Here's why:

* Heterozygous means having two different alleles for a specific gene. For example, having one allele for brown eyes (B) and one for blue eyes (b).

* Homozygous means having two identical alleles for a specific gene. This can be either homozygous dominant (BB) or homozygous recessive (bb).

Therefore, any individual with a genotype like BB or bb would be a non-example of heterozygous.

Other non-examples could be:

* A single-celled organism: These organisms do not have pairs of chromosomes and therefore cannot be heterozygous or homozygous.

* A trait determined by a single gene with only one allele: If there is only one allele for a trait, there's no possibility of having two different alleles, making heterozygosity impossible.

Remember, heterozygosity is specifically about having two different versions of a gene, so anything that doesn't fit that definition is a non-example.