How does one hear the difference between psi and psy? Would ten be used before a singular dog?
There is no difference in pronunciation between 'psi' and 'psy'.
If the cat sees one dog, you need to use the singular masc animate accusative form: 'psa'.
'Ten' (nominative form) would never be used in this sentence, you need to use the accusative here: 'toho' (sg) or 'ty' (pl).