Read Lips
To understand what someone is saying by reading lips, you must be within 30 feet of the speaker, be able to see him or her speak, and understand the speaker’s language. (This use of the skill is language-dependent.) The base DC is 15, but it increases for complex speech or an inarticulate speaker. You must maintain a line of sight to the lips being read.
If your Spot check succeeds, you can understand the general content of a minute’s worth of speaking, but you usually still miss certain details. If the check fails by 4 or less, you can’t read the speaker’s lips. If the check fails by 5 or more, you draw some incorrect conclusion about the speech. The check is rolled secretly in this case, so that you don’t know whether you succeeded or missed by 5.