What is the connotation of grin versus smile in the following passage?

"Were there any sheep in the park?" demanded Cyril.
"No;" said the bachelor, "there were no sheep."
"Why weren't there any sheep?" came the inevitable question arising out of that answer.
The aunt permitted herself a smile, which might almost have been described as a grin.

Smile is crueler than grin is.
Grin is kinder than smile is.
Smile is not as sincere as grin is.
Grin is more devious than smile is.