难 + Verb (unpleasant to …)

Hard to eat, hard to watch

• difficult / hard难nán means "difficult" — but stuck before a verb it builds handy adjectives.
• difficult / hard难nán + variant of 吃吃chī isn't quite "difficult to eat" — it means "tastes bad".
• It's the mirror image of good好hǎo (to be fond of eating好吃hǎo chī = tasty).

difficult / hard难nán + Verb = "unpleasant to (do)"

• difficult / hard难nán + Verb turns the action into a negative quality.

this这zhè(measure word)个gemedicine药yàovery很hěnbad-tasting难吃nán chī。

• very很hěnunpalatable难吃nán chī = "tastes bad" (hard to eat).

difficult / hard难nán vs good好hǎo

• difficult / hard难nán + Verb = unpleasant: ugly难看nán kàn (ugly), unpleasant to hear难听nán tīng (unpleasant to hear).
• good好hǎo + Verb = pleasant: good-looking好看hǎo kàn (good-looking), pleasant to hear好听hǎo tīng (nice to hear).

this这zhè(measure word)首shǒusong歌gēvery很hěnnice to hear好听hǎo tīng。

• pleasant to hear好听hǎo tīng = "sounds nice"; flip to unpleasant to hear难听nán tīng for "sounds awful."

Recap

Read the full reference: HSK 3 grammar — Verb phrases.