The default connection is a Bezier curve, it looks pretty and elegant except when it is too short. When the nodes are close together, the Bezier curve becomes a somewhat ugly and distractive S hook (that looks like a knot).
Suggestion: When the nodes are very close, less than a certain threshold. Bolt will use a straight line connection. A better and more sophisticated approach is to bring (scale by a portion) the control points MUCH closer to their respective nodes so the connection curve remain a very smooth curve leaving a node and entering the other node with essentially one tangential direction. I have tried this approach myself and the visual is very pleasing.
Customer support service by UserEcho