First, the meaning is different.
1, curling
It means bending and shrinking.
Curl up
It means that the body is curled up and tightened.
Second, the basic explanation is different.
1, curling
(1), boxing and contraction.
(2), metaphor is depressed.
Curl up
1. The body is curled up and tight. Kneeling, squatting, squatting, squatting.
2. don't stretch.
Third, the citation interpretation is different.
1, curling
Yang Mo's Flowers Everywhere in Spring City: "His thin body is curled up in a tattered sack."
Curl up
Jun Qing's Riverside at Dawn: "He was lying on a heatable adobe sleeping platform without a seat, covered with a dog skin and a straw cloak, curled up tightly together."