trash vs pick at

trash is a noun but pick at is not a noun.

Word	Noun	Adjective	Verb	Adverb
trash	Yes	No	Yes	No
pick at	No	No	Yes	No

As verbs, pick at is a hypernym of trash; that is, pick at is a word with a broader meaning than trash:

Other hypernyms of trash include belittle, disparage.

trash (noun)	pick at (noun)
an amphetamine derivative (trade name Methedrine) used in the form of a crystalline hydrochloride; used as a stimulant to the nervous system and as an appetite suppressant
nonsensical talk or writing
worthless people
worthless material that is to be disposed of

trash (verb)	pick at (verb)
express a totally negative opinion of	express a negative opinion of
dispose of (something useless or old)	eat like a bird
	pluck or pull at with the fingers