That’s because in English, verbs of perception (see, hear) are always simple present tense, not continuous, except in two situations:
1) if the thing one sees or hears is not actually real, but in a dream, imagination, or hallucinations, THEN we use “seeing things”, or I’m hearing strange noises, etc.
2) in the case of see, we can use it idiomatically to mean “meeting with regularly”.
So to say “the horse is seeing the cat” in English means that either the horse is imagining the cat, or they are dating each other... ;-).
No particular reason. There are several forms of German noun plurals— not all of them end in e.
1) Some nouns end in -e, and they form their plural by adding -n: Blume, Blumen; Katze, Katzen; Auge, Augen.
2) Some nouns don't end in -e, but add -e to form plural: Pferd, Pferde; Hund, Hunde; Tisch, Tische.
3) Some nouns add -e in the plural, AND change the vowel sound as well: Baum, Bäume; Stuhl, Stühle.
4) Some nouns add no ending in the plural, but only change the vowel sound: Vogel, Vögel.
5) Some nouns are the same in singular and plural: Fenster, Fenster.
That’s not all of the possibilities, but some of them anyway. If you check the Tips and Notes page for the Plurals lesson, and search online on German plural rules, you should have no trouble finding more.
In German, yes: Das Pferd sieht die Katze. In English, no: the verbs of perception (see, hear) are “stative” or “non-action” verbs, and they are not used in progressive forms except for certain idiomatic contexts.
If we say, “The horse is seeing the cat”, in English, it means either the horse is imagining a cat which isn’t there... or that the horse and the cat are dating each other!