John Gill Commentary 1 Samuel 1:12

"And it came to pass, as she continued praying before Jehovah, that Eli marked her mouth." — 1 Samuel 1:12 (ASV)

And it came to pass, as she continued praying before the Lord ,
&c.] Being very earnest and importunate with him to grant her request, and therefore repeated her petition, and prolonged her prayer, being unwilling to let the Lord go, until she had a promise, or some satisfaction, that she should have the thing she liked; some think she continued an hour in prayer:

that Eli marked her mouth ;
observed the motion of her lips, and no doubt her distorted countenance, and uplifted eyes and hands, but chiefly the former; not knowing what the woman was at, and what could be the meaning of such motions.