She turned the light low, and slipped stealthily over and knelt down by

the sack and felt of its ridgy sides with her hands, and fondled them lovingly

为什么是felt of (feel of) ？ 为什么有一个of ? 去掉of不行吗？

没看到动词短语feel of 用法? 老师讲解一下，好吗？ 谢谢！