those are not つ (tsu) but っ (sokuon). It indicates that the sound abruptly stopped. It's the same character you find in words which, when romanized, have a double consonant. For example, 逝ってよし = いってよし = itteyoshi.
Also remember to read right to left. "kyaru~n, kyapi~n, aha~n, hu~", etc. The circle on her head says "kochumochu", yeah. I wouldn't call it a "pun", though, just a cutesy sort of pronunciation of "kosumosu" which is the reading of "KOS-MOS", I assume.
