snarl vs snarl up

snarl is a noun but snarl up is not a noun.

Word	Noun	Adjective	Verb	Adverb
snarl	Yes	No	Yes	No
snarl up	No	No	Yes	No

As verbs, snarl and snarl up are synonyms defined as:

snarl and snarl up: make more complicated or confused through entanglements

Other synonyms of snarl include embrangle.

snarl (noun)	snarl up (noun)
something jumbled or confused
a vicious angry growl
an angry vicious expression

snarl (verb)	snarl up (verb)
make more complicated or confused through entanglements	make more complicated or confused through entanglements
utter in an angry, sharp, or abrupt tone
make a snarling noise or move with a snarling noise
twist together or entwine into a confusing mass