Like names that sound similar or begin with the same letter oooor have the same theme. (:
I've got: Olias and Olwin Evellyn and Etling Dredg and Daxton. Keets and Cloister both start with a 'k' sound.
How about you guys? :>
🦇🎃 [tt]selling current profile [/tt] 🦇🎃 - link
Letto and Amoretto are the big 'uns 8D; After i realized I did that, I've attempted to keep the rest of their names very different. XD
I have three names starting with an H and three starting with a V. Then there are 2x C, 2x F, 2x G, 2x M and 2x P.
[edit] Oh, and do name origins count as well? If so, I have four Pets named after characters from Norse mythology and five that are named after characters from Greek mythology.
Garth, Gordan, and Gulliver. Also, Lailah, Lawler, and Lucio.. x.x

I had Hiller, Myers and Miller, but got rid of Hiller because of that similarity. :(
I don't really have a name pattern to be honest. But I usually find a creative way of spelling ordinary names:
Oliver = Olyvir Aiden = Aydinn Elizabeth = Elyzabithe Alexander = Aylexsander
[ToT=Riley]
umm....
Alek and Arpeggio not that similar cept for the first letter XD Maia and Miriam again not that similar but the first letter Cadbury and Colin same as above. Roxy and Rae... yep nothin. Esther, Tori and Lyla don't have a letter buddy but I'm fine with that c:
I try not to have more than 2 pets with the same first letter. and it is damn hard sometimes DX
I have four Ts - Tripped, Tarke, Tenpou, and Tungl. I also have two Rs, Rheeta and Rosoff, two As, Alwir and Askea, and two Gs, Genissa and Gyoso. The Rs were supposed to match, the Ts, Gs, and the As are a coincidence though. Both As and both Gs start with different sounds though so they aren't really similar at all. Two of my other pets are based off characters in a story of mine - Jaymiz and Sayly. I don't try for themes really.
Holiday events
Err. Grammar nerd names, yes.
Apos - Apostrophe Hyph - Hyphen Colo - Colon Om - Comma Stet - Editing term meaning 'let it stand.'
Basically I'm an awesome person, okay? X_x
Countess, Corridor, and Celtic all begin with C. Aaaand Tank, Tabby, and Tar all start with 'Ta'.
Aside from that, mine are pretty diverse. :3
Letter-wise, not really.. I do have three T-names (Toby, Tatiana & Tomas), two L-names (Lärs & Lene), two A-names (Ania & Alexandros) ..
And that's it. xD
For general "name-ness" though, like 90% of my names come from Eastern Europe, or the general area around there. I have some westerners like Toby who is a Brit, and Matthieu who is French, but otherwise they're all crammed into the Eastern European states in terms of ethnic background. xD
None of mine sound tooo similar, but I do have 4 which start with a H u___u
I have Sabre, Stone and Sagittarius, but it's just a coincidence that they all start with the same letter xD
Since I often have two Pets starting with the same letter, I only list the ones I have most.
3 C - Claudandus, Caligula, Catull 3 M - Madcoil, Medullina, Millander 4 T - Taka, Taoist, The One Truth, Trajan
The only trend I see is that most of my pets have real human names. That and a lot of them are alternative spellings. Like I have Engelo instead of Angelo, Olivea instead of Olivia, Viviana instead of Vivian, Kalvin instead of Calvin.
I have a few pets with double-letters too: Juliette, Amoretta, Channelle.
I have Rich & Poor and Cuss & Fuss.
No matter what I do, I end up with similar pet names. I try to pick something that has nothing to do with any of my other pets' names and... turns out there's a similarity I didn't think of. ffffff.
I have four A's: Anneka Alistare Alanna Acrassicauda
five C's (and one K): Cater Callula Caris Carrie Corina Kar
I have three M's: Mark Merthin Manticore
Three S sounds: Succubi Sybil Iscaa
Philemon, Caris, and Merthin are all from the same book (World Without End by Ken Follett). Kar and Hannah, while they don't sound alike, are both named after me.
I can't help pet name trends. Whenever I think of a new name somehow it always sounds like/starts with the first letter/is related to a name I already have. The only pets I can think of that don't have any name similarities with the others are Devon and Edric AND EVEN THEY BOTH HAVE 'D' SOUNDS OMFG. D:
edit: they have D sounds, not had. durrdedurr.
EDIT AGAIN: OMFG I HAVE A DOUBLE LETTER TREND TOO JFC. Anneka Alanna Acrassicauda Carrie Callula Hannah Iscaa Succubi