└─$ for i in ./0{1..5}* ; do printf "\n$i\n========\n"; cat $i; done ; for i in ./06* ; do printf "\n$i\n========\n"; cat $i | grep -vE '^[a-z]{,3},' ; done

./01_200.csv
========
word,mirror

./02_1k.csv
========
word,mirror
do,in
no,on
so,an
not,one
use,hat

./03_5k.csv
========
word,mirror
do,in
on,no
not,one
use,hat
shoe,aunt
tide,edit

./04_10k.csv
========
word,mirror
do,in
on,no
so,an
not,one
set,ate
use,hat
mode,knit
shoe,aunt
tide,edit
whom,junk

./05_25k.csv
========
word,mirror
isis,dada
jute,whet
putt,ghee

./06_450k.csv
========
word,mirror
dits,idea
ditt,idee
dods,inia
does,inta
doit,inde
dops,inga
edge,tipt
edit,tide
eheu,tuth
ende,toit
enif,tody
ense,toat
fthm,yeuk
gnus,poha
gude,phit
hoes,unta
hoit,unde
ides,dita
init,dode
into,doen
isis,dada
isit,dade
isos,dana
itsy,deaf
jude,whit
just,whae
jute,whet
kept,mtge
knee,mott
knet,mote
mhos,kuna
mode,knit
mone,knot
mong,knop
muse,khat
muso,khan
mute,khet
nits,odea
ones,nota
onos,nona
phos,guna
phys,gufa
pose,gnat
psid,gadi
putt,ghee
sees,atta
shen,auto
shet,aute
shoe,aunt
shot,aune
shpt,auge
side,adit
sise,adat
sisi,adad
site,adet
sons,anoa
soon,anno
soot,anne
sops,anga
soso,anan
sunk,ahom
tees,etta
this,euda
tits,edea
tosk,enam
undo,hoin
ungt,hope
used,hati
usee,hatt
whin,judo
whom,junk
whot,june
dites,ideta
esses,taata
gnows,ponja
gunks,phoma
house,unhat
knoit,monde
musgu,khaph
mutis,kheda
shide,audit
sidth,adieu
singe,adopt
soote,annet
touse,enhat
whipt,judge
enosis,tonada
musked,khamti
sesses,ataata