24 Chapter 3identify the meaning of a dog’s bark, even if they have had very little experience
with dogs (Pongrácz et al., 2005). But the same is not true of the cat’s meow. Cat
owners can often distinguish the intention of their own cat’s meows but even indi-
viduals with extensive experience with cats appear to be less able to identify the
meaning of meows made by unfamiliar cats (Nicastro and Owren, 2003; Ellis et al.,
2015a). Meows therefore seem to be specific, not only to the context in which they
are performed, but also to the individual cat. This could be because cats are able
to learn, with repeated interaction and owner reinforcement, which sounds are
most likely to be recognized and produce the desired reactions from their human
caregivers.
A variation is the ‘silent meow’. The cat opens and closes its mouth in exactly
the same way as when producing a meow sound, and when directed towards people
it is usually in the same circumstances as a normal meow but no sound is produced,
at least not one that we can hear. Another difference is that the silent meow has
been noted to be a part of cat-to-cat communication between feral and farm cats
(Bradshaw et al., 2012). It is possible that a sound may be produced but at too high
a frequency for us to hear or it could be a part of visual signalling that we don’t, as
yet, fully understand.
The purr
The purr is produced by the contraction of the laryngeal muscles causing closure of
the glottis. As pressure builds it forces the glottis open and causes the separation of
the vocal folds, resulting in the purr. Unlike other vocalizations it is produced during
both inhalation and expiration and can occur alongside other vocal sounds (Remmers
and Gautier, 1972; Bradshaw et al., 2012).
Like the meow, the purr is a sound that pet cats commonly direct towards humans,
but unlike the meow it is also used in a wide range of cat-to-cat communication.
Purring seems to be more than a means of communication because it also occurs when
there are no other individuals, cat or human, around for the cat to communicate with
(Kiley-Worthington, 1984, cited in Bradshaw et al., 2012).
It has been found that pet cats produce two types of purr:
● The ‘unsolicitation’ purr is performed when the cat appears to be relaxed and
content, either alone or in relaxed social contact.
● The ‘solicitation’ purr is performed when the cat is anticipating or soliciting food
or attention. This purr also contains a higher pitched ‘cry’ and is reported as
sounding more ‘urgent’ and less pleasant to human ears. Like the meow, this
seems to be another form of specifically human-directed care-soliciting vocaliza-
tion (Bradshaw and Cameron-Beaumont, 2000; McComb et al., 2009).
Domestic cats are also known to purr when in extreme pain and even when
dying. One hypothesis is that the low frequency vibrations caused by purring have a
‘healing’ effect (Von Muggenthaler, 2006). Other suggestions are that purring in such
circumstances are a form of care or comfort soliciting or even possibly a form of
self-reassurance (Bradshaw, 1992; Bradshaw et al., 2012) but there is no scientific
evidence as yet to support any of these theories, so the reason why cats do this
remains unclear.