The usual small scales on the spike are in evolutionary terms modified leaves and some grass species occasionally 'remember' their past and elongate these scales (glumes and lemmas) into leaves.
This is known as Proliferation and occurs in grasses more frequently than in other plants. Sometimes the process is called Vivipary but this term should only apply to seeds that germinate in situ on the plant.
There are many theories why Proliferation occurs but it does seem to happen more towards the end of the flowering season. It seems the Florigen hormone has been used up producing normal flowers, so the plant goes into vegetative growth within the spikelets.
I have seen this often in Cocksfoot but never before in Timothy.
Proliferating Timothy Grass