Is Morris an untrustworthy guy?

I wouldn't say that Seargeant-Major Morris is at all untrustworthy. He warns the Whites, attempts to burn the paw, and tells them not to blame him for the consequences...... I'd say his words were an apt warning.

"Better let it burn," said the soldier, solemnly.

"If you don't want it, Morris," said the other, "give it to me."

"I won't," said his friend, doggedly. "I threw it on the fire. If you
keep it, don't blame me for what happens. Pitch it on the fire again
like a sensible man."

The other shook his head and examined his new possession closely. "How
do you do it?" he inquired.

"Hold it up in your right hand and wish aloud," said the sergeant-major,
"but I warn you of the consequences."