The affix ṭac comes after the word śvan ending in a tat-puruṣa samāsa when another thing not being a living object is compared with it.,
Thus आकर्षः श्वेव = आकर्षश्वः 'a dog-like bow'. फलकश्वः \a dog-like blade\. This compounding takes place by 2.1.56.
Why do we say \when something is likened to it\? Observe न श्वा = अश्वा लोष्टः \a clod of earth which is not a dog\. This is not a very happy counter-example of Kasika : for in the case of नञ् Tatpurusha compound there is express prohibition taught in 5.4.71. The proper example should be निःश्वालोष्टः ॥ Why do we say \when the thing compared is not a living being\ ? Observe वानरः श्वेव = वानरश्वा \a dog-like monkey\.,