Syriac is a joined script, written right to left, and most of its letters connect to the letter on either side. Eight do not connect to the letter that follows: alaph, dalath, he, waw, zain, sadhe, rish and taw. After one of these the pen lifts and the next letter starts a fresh connected group.
This is not a defect and it is not decoration. It gives a page of Syriac its visible structure. Word boundaries in Syriac are marked by spacing, which in a cursive hand can be slight, so the breaks inside words are what keep a line from reading as one continuous stroke. A practised reader uses them to segment the line before recognising any individual letter.
Zain is one of the eight, which matters more than usual for this particular letter, because zain, dalath and rish are so similar in the older hand. A reader who has already identified a break knows something about what can be sitting at that break, which narrows the field before the shape has to be judged at all.
The same behaviour appears in Arabic, where a comparable set of letters joins only to the right, and in Mandaic, where a comparable but not identical set does. The three scripts inherited the habit along with the alphabet, and each settled its own list. Comparing the lists is one of the few places where the descent of these scripts can be seen in how they are written rather than in what order the letters come.