What does “all senses cocked” mean?

Solution 1:

This probably comes from the phrase 'cocking the gun' which means to ready the gun to fire. 'Senses cocked' would then translate to very alert or charged senses.

Solution 2:

It's not unusual to cock your head, or sometimes to cock your ears to hear something better. Collins (senses 3/4) says that this use is a synonym of prick up or point, so that only animals can genuinely cock their ears, and birds frequently cock their heads, whether male or female. Cocking all senses is an extension of this - whether an exciting metaphor or a step too far from someone who doesn't know the derivation is a personal choice.

Solution 3:

In a comment, John Lawler wrote:

The OED says both the sense of cock the head/hat and the sense of cock the hammer/pistol come from the characteristic motion (and in the case of early firearms, the characteristic shape) of a cock's head. Roosters used to be more obvious and common as examples for metaphors than they are today.